Question: how to install quake on mac?
Answer: install the quake client from here.
download the shareware version of quake here.
unzip the . ... 
then open up glquake.
it will ask you to locate the ID1 folder, find it (it should have PAK0. ... 
It will load if correctly found ID1 folder is selected.
Press the green play button.
Have fun playing old school quake!