Here is the workflow for using Github for the non-committers who are developing their features on GitHub:

#1. Create an account on GitHub.
See Setting Up Git
#2. Fork the Apache Repo:
#a. Go to https://github.com/apache/incubator-cloudstack.
#b. Click Fork.
See Fork a Repo
#3. Clone your fork:
git clone https://github.com/<username>/incubator-cloudstack.git
#4. Configure remote:
git remote add upstream https://github.com/apache/incubator-cloudstack

Now, you are ready to go. You can pull the changes from upsteam, create branches, push the changes to origin.