So, what is Git in a nutshell?
This is an important section to absorb, because if you understand what Git is and the fundamentals of how it works, then using Git effectively will probably be much easier for you. As you learn Git, try to clear your mind of the things you may know about other VCSs, such as Subversion and Perforce. Doing so will help you avoid subtle confusion when using the tool.
Git stores and thinks about information much differently than those other systems. Even though the user interface is fairly similar, and understanding those differences will help prevent you from becoming confused while using it.