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Step - 1 : Create the sub-directory in hot-deploy/ and name it "practice"(hot-deploy/practice). The directory name should match the new components name that we are creating.
Note : Remember all customized development is done at this place only. 
Step - 2 : Create the ofbiz-component.xml file on path hot-deploy/practice and place following content in it (for reference you can check this file in any other component of OFBiz):

<?xml version="1.0" encoding="UTF-8"?>
<ofbiz-component name="practice"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:noNamespaceSchemaLocation="http://ofbiz.apache.org/dtds/ofbiz-component.xsd">
      <resource-loader 	name="main" type="component"/>
    <webapp name="practice"
       title="Practice"
       server="default-server"
       base-permission="OFBTOOLS"
       location="webapp/practice"
       mount-point="/practice"
       app-bar-display="false"/>
</ofbiz-component>

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1. The ofbiz-component.xml file is responsible for letting OFBiz know where resources are at as well as allowing you to add to the classpath.
2. Here 'resource-loader name' can be any string here it is "main". The 'type' tells OFBiz that we will be loading a component.

<resource-loader name="main" type="component"/>

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Step - 1 : Create a "webapp" directory in the practice component (hot-deploy/practice/webapp).
This directory contains all the webapp related files for the component we are creating.
Step - 2 : Create a sub-directory inside the webapp directory by the name of  "practice" which is the name of the webapp which you are going to develop (hot-deploy/practice/webapp/practice). A component can have multiple webapps attached to it. e.g. In the "marketing" component there are two webapps "marketing" and "sfa".
The webapp we are creating will follow the J2EE webapp standards.
Step - 3 : Create WEB-INF directory in your webapp (hot-deploy/practice/webapp/practice/WEB-INF).
An OFBiz web application requires two configuration files, a controller.xml and a web.xml. The controller.xml tells OFBiz what to do with various requests from visitors: what actions to take and what  pages to render. web.xml tells OFBiz what resources (database and business logic access) are available for this web application and how to handle web-related issues, such as welcome pages, redirects, and error pages.
Step - 4 Create a file named "web.xml"(web.xml follows j2ee webapp specs). Contents of this file can be taken from any of the existing component e.g. example component. The Important values to change are the <display-name>, the localDispatcherName, and the mainDecoratorLocation.   

<context-param>
     <param-name>localDispatcherName</param-name>
     <param-value>practice</param-value>
     <description>A unique name used to identify/recognize the local dispatcher for the Service Engine</description>
</context-param>
<context-param>
     <param-name>mainDecoratorLocation</param-name>
     <param-value>component://practice/widget/CommonScreens.xml</param-value>
     <description>The location of the main-decorator screen to use for this webapp; referred to as a context variable in screen def XML files.</description>
</context-param> 

For now put the value: "component://practice/widget/CommonScreens.xml" in for the location and you will see why in a while. This location is used in pointing to the main decorator location in screens like

${parameters.mainDecoratorLocation}

Which increases the code Independence from changing the path at many places when we need to change the main decorator location. At that time we just need to change the location there only and will work for all the screens where it has been used. One more advantage of doing this in screens is the purpose of resuability of existing screens which we can use from other components, but it decorate that screen by your decorator only as the same pattern is used at all the places and in all the components to show the mainDecoratorLocation. Concentrate on this when you add decorators in your screens in not too distant future with the development of this application.

Step - 5 Create a file named "controller.xml" (used by ofbiz webapp controller)  This file will be small and simple at first but will grow as we add functionality later on. For now insert the following code:

<?xml version="1.0" encoding="UTF-8"?>
<site-conf xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xsi:noNamespaceSchemaLocation="http://ofbiz.apache.org/dtds/site-conf.xsd">
       <include location="component://common/webcommon/WEB-INF/common-controller.xml"/>
       <description>Practice Component Site Configuration File</description>
       <owner>Copyright 2001-2008 The Apache Software Foundation</owner>
       <!-- Request Mappings -->
       <request-map uri="main">
           <security https="false" auth="false"/>
           <response name="success" type="view" value="main"/>
       </request-map>
       <!-- end of request mappings -->
       <!-- View Mappings -->
       <view-map name="main" type="screen" page="component://practice/widget/PracticeScreens.xml#main"/>
       <!-- end of view mappings -->
</site-conf>

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*Step - 1 :*For this create directory by name "config" in your component directory i.e. "practice".
Note: -Here remember to create an entry for the config directory in your ofbiz-component.xml file.
which will be :

<classpath type="dir" location="config"/>

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That means you have to place the config directory on the classpath to access configuration files.

Step - 2: Now create a file by name PracticeUiLabels.xml and create some of the ui labels for practice applicaton. (take reference from ExampleUiLabels.xml). Here remember one thing whenever you make a change in UiLabels then you have to restart the server for having the changes in effect. At first create only 2 ui labels like

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Step - 1 :  Take reference from ExampleMenus.xml file for having login and logout options in your menu.
Targets for these options will be available from "component://common/webcommon/WEB-INF/common-controller.xml", which we have to include in our controller.xml.
or you can do these entries in your controller.xml file under

<!- Request Mappings ->
<!-- Security Mappings -->
 <request-map uri="checkLogin" edit="false">
    <description>Verify a user is logged in.</description>
        <security https="true" auth="false"/>
        <event type="java" path="org.ofbiz.webapp.control.LoginWorker" invoke="checkLogin" />
        <response name="success" type="view" value="main"/>
        <response name="error" type="view" value="login"/>
    </request-map>
    <request-map uri="login">
        <security https="true" auth="false"/>
        <event type="java" path="org.ofbiz.webapp.control.LoginWorker" invoke="login"/>
        <response name="success" type="view" value="main"/>
        <response name="error" type="view" value="login"/>
    </request-map>
    <request-map uri="logout">
        <security https="true" auth="true"/>
        <event type="java" path="org.ofbiz.webapp.control.LoginWorker" invoke="logout"/>
        <response name="success" type="request" value="checkLogin"/>
        <response name="error" type="view" value="main"/>
    </request-map>

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Step - 1: Create directory by name "servicedef" in component directory "practice". This directory will contain all the service definition files e.g. services.xml, secas.xml.
Note :  If it is a service which is written in Java then it will be placed in "src" directory and if it is a service which is written in minilang then it will be placed in script directory. e.g. for java applications/party/src/org/ofbiz/party/party/PartyServices.java and for minilang applications/party/script/org/ofbiz/party/party/PartyInvitationServices.xml. Respective class path and file path will be mentioned in the service definition.
*Step - 2 :*In controller you have to create an entry for the request for the execution of a service and set the response like

<request-map uri="createPracticePerson">
    <security https="true" auth="true"/>
    <event type="service" invoke="createPracticePerson"/>
    <response name="success" type="view" value="PersonForm"/>
</request-map>

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First we will be writing services for Party then while writing services for creating Person we will be calling the service for party.
Step - 1 :Create a file by name "services.xml" in servicedef directory.
Step - 2 : Define services for CRUD operations for Party entity. Name of services will be createPracticeParty, updatePracticeParty, deletePracticeParty and specify the correct location to the file where these services will be implemented like /framework/example/script/org/ofbiz/example/example/ExampleServices.xml.
Step - 3 : Create directory structure and PracticeServices.xml file in your component directory for giving the implementation of these services.
(For implementation take reference from service.xml and ExampleServices.xml files of Example component)
Note : Do not use the <override> tag as it is introduced later in the tutorial. 
From this place if you want to run these services then you can run them by webtools--> Run Service . By this place you can test your services.
Note: At this place you must read http://www.nabble.com/The-fancy-new-entity-auto-service-execution-engine-td18674040.html. This feature has been recently added against the traditional approach of writing CRUD operations for an entity.
This new feature enables you to just define the services by mentioning the operation you want to perform.Basically just set the engine attribute to "entity-auto" and the invoke attribute to "create", "update", or "delete".
like you can take a look in the following code from services.xml of example component:  

<service name="createExample" default-entity-name="Example" engine="entity-auto" invoke="create" auth="true">
    <description>Create a Example</description>
    <permission-service service-name="exampleGenericPermission" main-action="CREATE"/>
    <auto-attributes include="pk" mode="OUT" optional="false"/>
    <auto-attributes include="nonpk" mode="IN" optional="true"/>
    <override name="exampleTypeId" optional="false"/>
    <override name="statusId" optional="false"/>
    <override name="exampleName" optional="false"/>
</service>

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Events can be written in Java and minilang both. Now the next development which you are going to do will be writting these events.
Events are used for the validation and conversion using Simple Map Processor. The Simple Map Processor Mini-Language performs two primary tasks: validation and conversion. It does this in a context of moving values from one Map to another. The input map will commonly contain Strings, but can contain other object types like Integer, Long, Float, Double, java.sql.Date, Time, and Timestamp.
Before moving any further an important link to go through is : http://docs.ofbiz.org/display/OFBIZ/Mini-Language+Guide#Mini-LanguageGuide-smapFor making an understanding with it implementation will be done by performing following steps:
Step - 1 : For this create another tab in your practice application menu bar for this by Name "Events".
Step - 2 : Now create another menu with two menu item in PracticeMenus.xml file by name "EventMenu". This menu will be having 2 menu Item one will be by name "EventMinilang" and  another by name "EventJava". One will be used to show the form which we will be calling an event which will be in minilang and other will be used to call java event.
Step - 3 : Simply show form on the request of both which will be for creating a new person. Both the forms will be different for calling different events as target in them.
Step - 4 : Show labels in screens above the form like "New Person - Simple Event"  and  "New Person - Java Event" so that it will be easy to identify the purpose of that form.
Step - 5 : Now set event in target of the forms and create request mappings in controller for the event.
Here important thing to note is in case of simple event controller entry will be like :

<request-map uri="createPracticePersonSimpleEvent">
    <security https="true" auth="true"/>{color}
    <event type="simple" path="org/hotwax/practice/PracticeEvents.xml" invoke="createPracticePersonSimpleEvent"/>
    <response name="success" type="view" value="CreatePracPersonSimpleEvent"/>
    <response name="error" type="view" value="CreatePracPersonSimpleEvent"/>
</request-map>

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Step - 6 : Now in the script/org/hotwax/practice/ create one file by name PracticeEvents.xml.
Step - 7 : Write the event in PracticeEvents.xml file by name createPracticePersonSimpleEvent.(For reference you can go through the event "createUser" from UserEvents.xml from party component)
The event which you will be writing should be the simple one as you just have to process 5 fields coming from the form which are salutation, firstName, middleName, lastName, suffix. and then you have to call the createPracticePerson service.
For processing the field you will be using simple map processor as you have read earlier. 
Follow these steps for writing the event:
7.a : Process fields coming from the form like: 

<call-map-processor in-map-name="parameters" out-map-name="createPersonContext">
    <simple-map-processor name="createPersonMap">
        <process field="firstName">
            <copy/>
            <not-empty>
                <fail-property property="PracticeFirstNameMissingError" resource="PracticeUiLabels"/>
            </not-empty>&nbsp;&nbsp;&nbsp;
        </process>
    </simple-map-processor>
</call-map-processor>
<check-errors/>

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Here the java event which you will be writing will be fairly simple. For reference you can check any of the *Events.java file.
Step - 1 : The contents will be :

public static String createPracticePersonJavaEvent(HttpServletRequest request, HttpServletResponse response){
    LocalDispatcher dispatcher = (LocalDispatcher) request.getAttribute("dispatcher");
    GenericDelegator delegator = (GenericDelegator) request.getAttribute("delegator");
}

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Step - 1 : For this you have to write another service by name "createPartyRoleVisitor",  which will be setting the role for the party which will be created by "createPracticePerson" service.
The service "createPartyRoleVisitor" will be triggered by the seca rule which you will define for service "createPracticePerson".
In the new service involved entity will by "PartyRole". In "createPartyRoleVisitor" just call service "createPartyRole" which is already implemented.
Step - 2 :  Now you have to create a file by name "secas.xml" in "servicedef" directory. Seca definition will come here. (Take reference from secas.xml of "party" component). This will be

<eca service="createPracticePerson" event="commit">
    <condition field-name="partyId" operator="is-not-empty"/>
    <action service="createPartyRoleVisitor" mode="sync"/>
</eca>

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Step - 1 : For this you have to write another service by name "createPartyRoleCustomer",  which will be setting the role for the party which will be created means when a record for the entity "Party" will be created this service will be triggered for setting a role customer for that party. The service "createPartyRoleCustomer" will be similar to "createPartyRoleVisitor".
Step - 2 :  Now you have to create a file by name "eecas.xml" in "entitydef" directory, which will be in your component directory "practice". Eeca definition will come here. (Take reference from eecas.xml of "accounting" component). This will be :

<!-- To create party role whenever a party is created -->
<eca entity="Party" operation="create" event="return">
    <condition field-name="partyId" operator="is-not-empty"/>
    <action service="createPartyRoleCustomer" mode="sync"/>
</eca>

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    Group services are used to call more then one services as a group. Service groups are a set of services which should run when calling the initial service. You define a service using the group service engine, and include all the parameters/attributes needed for all the services in the group. The location attribute is not needed for groupservices, the invoke attribute defines the name of the group to run. When this service is invoked the group is called and the services defined in the group are called as defined.
For mor details on this visit :  http://docs.ofbiz.org/display/OFBTECH/Service+Engine+Guide
For the implementation of Group service follow these steps: 
Step - 1 : Add another menu item to applicatoin menu bar by name "Group Service".(Do the needful entries for target in controller.xml)
Step - 2 : Now create new screen and a form for creation of the person because the target for the form will be the group service which we will be defining.
Note : Now the time is to define the group service. We will be defining the group service for the services which we have implemented for this practice application.
Step - 3 : You will be defining the service group in services.xml file.(Take reference from services.xml of party component).
Just write one more service which will be setting the role "CLIENT" for the party which will be created by createPracticePerson Service. 
 Create a group service by name "partyGroup" like :

<!-- Group service -->
<service name="partyGroup" engine="group" auth="true">
    <description>Creates a party, person and party role Client</description>
    <group>
        <invoke name="createPracticePerson" result-to-context="true"/>
        <invoke name="createPartyRoleClient"/>
    </group>
</service>

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The interface service engine has been implemented to help with defining services which share a number of the same parameters. An interface service cannot be invoked, but rather is a defined service which other services inherit from. Each interface service will be defined using the interface engine.
For more details on this visit :  http://docs.ofbiz.org/display/OFBTECH/Service+Engine+Guide
For implemeting the interface follow these steps:
Step - 1 : Add another menu item to applicatoin menu bar by name "Interface".(Do the needful entries for target in controller.xml)
Step - 2 : Create new screen, form and service for creating a person. Here service will implement the interface. (For creating interface take reference from services_fixedasset.xml of accounting component) it will be like :

<!-- Peson Interface -->
<service name="createPersonInterface" engine="interface" location="" invoke="">
    <attribute name="firstName" mode="IN" type="String" optional="false"/>
    <attribute name="middleName" mode="IN" type="String" optional="true"/>
    <attribute name="lastName" mode="IN" type="String" optional="false"/>
    <attribute name="suffix" mode="IN" type="String" optional="true"/>
</service>
<service name="createPracticePersonInterfaceService" engine="simple"
        location="org/hotwax/practice/PracticeServices.xml" invoke="createPracticePersonInterfaceService" auth="false">
    <description>Creates a new Person</description>
    <implements service="createPersonInterface"/>
    <attribute name="partyId" mode="OUT" type="String" optional="false"/>
    <override name="suffix" optional="false"/>
</service>

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 For the creation of new entity you can again take a referecne from example component for this you can have a look in entitymodel.xml file of example component. You can create new entities by following these steps:
Step - 1 : Create a new subdirectory by name entitydef in hot-deploy/practice/.
Step - 2 : Create new file by name  entitymodel.xml. This file will contain the defintions of entities which you want to define.
Step - 3 : For loading the defintion you need to do an entry in your ofbiz-component.xml file like:

<entity-resource type="model" reader-name="main" loader="main" location="entitydef/entitymodel.xml"/>

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Yes you can extend an existing entity for adding more fields to for your custom needs. This can be done in following way:
Step - 1 :  For extending an entity you can do in this manner in the entitydef/entitymodel.xml file of your custom application.

<extend-entity entity-name="">
    <field name="" type=""/>
</extend-entity>

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 For preparing data for your practice application following steps can be performed:
Step - 1 : Create new folder in practice by name "data" and create a file in it by name PracticeData.xml.
Step - 2 : Now we are going to create the data for a user for this we have to prepare it in a specific order for a party like :

<?xml version="1.0" encoding="UTF-8"?>
<entity-engine-xml>
    <Party partyId="DemoUser" partyTypeId="PERSON"/>
    <Person partyId="DemoUser" firstName="Practice" lastName="Person"/>
    <PartyRole partyId="DemoUser" roleTypeId="VISITOR"/>
    <ContactMech contactMechId="5000" contactMechTypeId="EMAIL_ADDRESS" infoString="practice.person@gmail.com"/>
    <PartyContactMech partyId="DemoUser" contactMechId="5000" fromDate="2001-05-13 00:00:00.000" allowSolicitation="Y"/>
    <PartyContactMechPurpose partyId="DemoUser" contactMechId="5000" contactMechPurposeTypeId="PRIMARY_EMAIL" fromDate="2001-05-13 00:00:00.000"/>
</entity-engine-xml>

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