Learn the basic concepts of of version control using git and Github.
Thanks to Tower (a Git GUI) I also handed out cheat sheets. Get a copy here:
Note: The message around what git-blame is and why it's awesome does not appear in this static version since it was improvised. Short version: Git-blame provides an annotated, line-by-line commit history for the file. For best results, click the "Blame" button when looking at any file on Github to unleash the awesomeness that is git-blame.