The entire Pro Git book, written by Scott Chacon and published by Apress, is available online for free. All content is licensed under the Creative Commons Attribution Non Commercial Share Alike 3.0 license. Print versions of the book are also available on Amazon.com.
In this book, Andrew Burgess will take you from knowing nothing about source code management to being able to use Git proficiently.
Get up to speed on Git for tracking, branching, merging, and managing code revisions. Through a series of step-by-step tutorials, this practical guide takes you quickly from Git fundamentals to advanced techniques, and provides friendly yet rigorous advice for navigating the many functions of this open source version control system.