Mere moments ago, quoth I:
When you're looking at any existing repository on GitHub there's a "clone URL" shown on the right hand side, which you can use if you want to make a clone on your local PC using standard Git tools. This typically is *not* what you want to do initially, though.
I should qualify that: you typically should not use the clone URL for a repository in which you intend to make public changes but you do not have rights to push. It's ok to clone something when you're just wanting read-only access (or at least you never intend to publish changes publicly), or if you do have rights to push (possibly because you've created your own fork of the "real" repository). (This isn't a hard rule of course, but as a guideline it makes life easier.)