Why use Git, because Git is distributed so you have the ability to have a copy of the complete repository on your local drive that you can work against.
The git object types are blob, tree, commit, and tag. This page gives a detailed overview of each of these types. A deep dive on each can be found here as well.
Git provides better history, flexibility in where you work, easy branching, is flexible and powerful, and it is FAST. 30+ FREE tutorials at GitGuys.com.
The git "index" is where you place files you want committed to the git repository. Learn more about the git index and git commit by selecting this link.
