See brief intro for the specific Torque2D project, which suggests seeing the following
Recommended reading
The Git Reference docs explain everything about Git with really clear examples : http://gitref.org/index.html
I strongly suggest bookmarking http://www.kernel.org/pub//software/scm/git/docs/ for the most direct and complete information on each command.
You can also run through this amazing and simple tutorial. It looks deceptively simple but it teaches you everything you need to know about using Git : http://rogerdudler.github.com/git-guide/
You can also download the 'Git cheatsheet' and keep it handy : http://rogerdudler.github.com/git-guide/files/git_cheat_sheet.pdf