Without a doubt, this is the most comprehensive documentation of using Git there is. Below is the list of chapters as outlined in the BOOK section of the resource site.
Also, be sure to look into additional resources like:
The entire Pro Git book, written by Scott Chacon and published by Apress, is available here. All content is licensed under the Creative Commons Attribution Non Commercial Share Alike 3.0 license. Print versions of the book are available on Amazon.com.