Download and install Git: http://git-scm.com/downloads
Download and install the JDK: http://www.oracle.com/technetwork/java/javase/downloads/index.html
Download Eclipse: http://www.eclipse.org/downloads/
Unzip eclipse and run the eclipse.exe contained within the folder. Create a workspace. In eclipse goto Window -> Preferences -> Java -> Installed JREs and add the JDK you installed. It will most likely be in C://Program Files/Java/jdk.1.X.XX
Next part is to fork the repo, just follow the directions on github https://help.github.com/articles/fork-a-repo