Git for User Assistance Developers
The Eclipse User Assistance source repository will be in Git starting late August 2011.
Getting Started with Git
If you are not familiar with Git you should start by reading up on it.
Pro Git is an excellent book which describes the concepts behind Git and how to use Git from the command line. It does not cover EGit, the Eclipse Git integration.
EGit is the home page for the EGit project. EGit provides the UI for working with Git in Eclipse.