Here is a nice guide you can try straight in your browser: http://try.github.io
Also, give a read to: http://sixrevisions.com/web-development/easy-git-tutorial/
If you are able to complete this: http://pcottle.github.io/learnGitBranching/?demo, then you are a git guru:) Just go through things and the way they are explained, they are quite simple.
You might want to try http://www.codeschool.com/courses/git-real as well.
These are just resoueces. You do not need all of them. Choose one or two. The secret is practice.