Git is a very handy tool to manage revisions of code and files. Any web developer should use a system like git. Why? Because copying complete folder to keep revisions of a website are not really a clean way of doing.
There are plenty of good resources out there explaining what git (and mercurial and svn) can do for developers, but until now the learning wasn’t that fun. Not anymore, since GitHub has released their new 15 Minute tryGit interactive lessons.
I love the approach which includes guidance, a virtual terminal window, a repository view and a funny advice panel.
cheat sheet : http://byte.kde.org/~zrusin/git/
resource : https://github.com/training/free