Git is a version control system that allows groups of people to work on the same documents without making a mess. Note: although this is not necessary, you should sign up for GItHub. It provides free git hosting. Also, most ruby/JS projects are hosted there and it is a great place to find new stuff.
- Try Git- This is a great 15 minutes introductory test drive to Github.
- Git Immersion - This is a guided walkthrough that will teach you the fundamentals of Git.
- Git For Ages 4 And Up - Great video to understand how Git works and what is going on each time you commit, branch, etc...
- Pro Git - The entire book can be read online