Git isn't a version control system. No fancy acronym, that's just what Linus says. Still, he wrote it and uses it to keep track of versions of the kernel. This presentation will be one big usage example of git. Knowledge in other VCSs (cvs, subversion, others) is recommended, but optional. Also recommended but optional is viewing Linus's talk on motivation for writing (and using) git: http://www.youtube.com/watch?v=4XpnKHJAok8