See Using pull requests.
Use the Github interface to fork https://github.com/CynderTech/git-tutorial to your GitHub account.
From the command line:
git clone git@github.com:<your_github_username>/git-tutorial.git
Now you have a working copy of the repository.
Donal says: I always use the git@ (= git:// over SSH) protocol for any
repo I own. I find it easier to set up an SSH key than manage
username/password. It's faster and less flakier than the https:// protocol.
By the way, never use the git:// protocol by itself. It doesn't have
authentication.