How to use Git?

Have a look at git for designers for great one page article/high level intro to the topic. (That link is broken: Here is a link to another Git for Designers )

I would start at http://git-scm.com/documentation, there are documents and great video presentations for non-software-developer/cs users. Git for beginners have some basic stuff.

I really like the O'Reilly book "Version Control with Git". I read it cover-to-cover and now I'm very comfortable with advanced git topics.