I have no idea about the installation on mac but its likely the same as in windows.
-Go to mods on the top bar and search the mod you want.
-Open it by clicking the name or right click open in a new tab
-Copy all the code you see and save it as a tbm file with the name of the mod "blablabla".tbm
-Finally place this file in your toribash/data/mod folder
Have fun