What is the difference between doing (after mkdir repo and cd repo):
git init
git remote add origin git://github.com/cmcculloh/repo
git clone means you are making a copy of the repository in your system.
git fork means you are copying the repository to your Github account.
git pull means you are fetching the last modified repository.
git push means you are returning the repository after modifying it.
In layman's term:
git clone is downloading and git pull is refreshing.