Navigating to your steam folder on mac for where the games are is a headache.
Easiest thing to do
a) Launch Steam
b) Select Any game from the library
c) Right click game > Properties
d) Click on Local Files Tab and click Browse Local Files
Easiest way to get to the folder where your games are.
Otherwise its
Users/(YOUR USERNAME HERE)/Library/Application Support/Steam/SteamApps/common/(NAME OF YOUR GAME FOLDER)