I had to learn git not too long ago, and found "Git from the bottom up" [1] to be immensely helpful. Until about halfway through reading it I was totally lost, but then everything started to click into place. I had a lot of trouble using git without that decent understanding of the whole system.

This seems like a great guide for people who only need a quick crash course in the specifics of actually using git, but for anyone who still feels lost without that deeper grasp, I definitely recommend "Git from the bottom up".

[1] http://ftp.newartisans.com/pub/git.from.bottom.up.pdf