I installed Git using MacPorts with
sudo port install git-core.
After installing Git, I installed the Git bundle for TextMate.
I signed up for Git hosting at GitHub. The process is nearly self-explanatory but I consulted two tutorials, A Tutorial Introduction to Git and Setting up a new Rails app with Git. I discovered I needed to create an ssh public/private key pair on my local machine and add the public key to my GitHub profile before I could push the app to the GitHub repository.