For those who don't know Git is a version control system developed by Linus Torvalds. It's main difference from other tools like SVN and CVS is the fact that it's distributed.
Recently I gave a workshop about Git here at the company where I walked through the most common cases I usually see when working in a team and thought about posting a summary of the commands used in the workshop.
It turns out that just this morning I found this - a.k.a the rest of my post. It's a really nice and concise Git Cheat Sheet that covers most of what I talked about in the workshop. So I highly recommend you bookmark it. It will certainly be useful.