I found a fantastic answer here:
As you probably know, git is a distributed version control system. Most operations are done locally. To communicate with the outside world, git uses what are called remotes. These are repositories other than the one on your local disk which you can push your changes into (so that other people can see them) or pull from (so that you can get others changes). The command
git remote add origin git@github.com:peter/first_app.gitcreates a new remote called origin located atgit@github.com:peter/first_app.git. Once you do this, in your push commands, you can push to origin instead of typing out the whole URL.
I would recommend reading the whole answer.