Confusion with -git- instructions

192:tmp red_angel$
192:tmp red_angel$ mkdir gts01
192:tmp red_angel$ cd gts01
192:gts01 red_angel$ # Now I initialize the GIT repository
192:gts01 red_angel$ git init
Initialized empty Git repository in /Users/red_angel/tmp/gts01/.git/
192:gts01 red_angel$
192:gts01 red_angel$ # Now I attempt (as I understand) to follow your instructions.
192:gts01 red_angel$ git fetch https://github.com/sophiaphillyqueen/testy.git
remote: Counting objects: 14, done.
remote: Compressing objects: 100% (11/11), done.
remote: Total 14 (delta 3), reused 12 (delta 1)
Unpacking objects: 100% (14/14), done.
From https://github.com/sophiaphillyqueen/testy
 * branch            HEAD       -> FETCH_HEAD
192:gts01 red_angel$ git checkout https://github.com/sophiaphillyqueen/testy.git/master
error: pathspec 'https://github.com/sophiaphillyqueen/testy.git/master' did not match any file(s) known to git.
192:gts01 red_angel$
192:gts01 red_angel$
192:gts01 red_angel$ # Clearly, there is something I am missing.
192:gts01 red_angel$
192:gts01 red_angel$