Newbie please help.

Hi all,
I am a newbie to git.
Do we have any documentation for the usage of git.  Basically i have
downloaded open-fcoe project into my machine,  i want to roll back to
the earlier version.  I  want some documents which gives a list of
command to be used to see the different versions and download the
somewhat older/stable version.

Thanks in Advance.

~Cheers
Prasanna