Dave,
I am honestly a little lost at which point you are (since someone already pointed the user you are trying doesn't even exists) and what you are trying to do so my answer will go from the beginning just in case.
Since I noticed you are using it on a MAC, you might want to try http://mac.github.com/ which should give you an easier time for begginers.
If you want to really go using your console, this might help (http://gitref.org/creating/).
Perhaps the easiest way was just to go to the project you are interested and click 'Fork' on the web browser, this would get you the project on your remote repository, and would allow a way to contribute back to the project as stated on (http://stackoverflow.com/questions/6286571/git-fork-is-git-clone)
If you still want to stick with clone for another reason, make sure you get the right link on the project page at github and run the command.
Hope this helps.