Git Immersion is a guided tour that walks through the fundamentals of Git, inspired by the premise that to know a thing is to do it.
Git is a powerful, sophisticated system for distributed version control. Gaining an understanding of its features opens to developers a new and liberating approach to source code management. The surest path to mastering Git is to immerse oneself in its utilities and operations, to experience it first-hand.
via gitimmersion.com
A nicely done tutorial that takes you through all aspects of git on a guided tour