Here are resources I collected for how to use Git to collaborate. I hope these tutorials will help you understand how to pull the latest source code and fork/pull request to contribute to this project!
Fork/Pull request
Tutorials of a nice Git GUI: SourceTree
Getting started with Git using SourceTree
If you are as lazy as me (don't want to type any command when using Git) you would love "SourceTree".
Learn Git In 15 Minutes
A short intro to Git
Git & GitHub Tutorial for Beginners
A more hands-on tutorial on how to use GitHub. ~ 10mins each
Git & GitHub Crash Course For Beginners
A very general/detailed crash course explaining what is Git. ~30mins long
tutorials
git
COSMOSS