I'm getting closer, but I'm confused. What was the whole point of setting up an SSH key if they are asking me for a password?

You are getting closer because now your repo has something in it, so that's better.

You have set up a remote which uses https instead of ssh. Use git remote -v to show the remote URLs and you will see this. Change them to be ssh remotes instead so that you can use your key pair and you should be good to go.