Hi breasal, I don't own a Mac so I cannot test this, but Mac runs unix shell so it should be relatively simple to do even without terminal.
First, make sure that you're running latest Java. You can check that from the browser - https://java.com/en/download/installed.jsp
Grab latest IRI, unzip, then create a text file inside of the IRI folder, and save it for instance as IOTA.command with this content:
java -jar IRI.jar
read -p 'IRI terminated. Hit Enter to continue'
the last line should allow you to see errors in console window if the process crashes.
Maybe you can now run IRI already with double-clicking the IOTA.command file you saved. If it does not run, you may need to use once a shell window, go to your IRI folder, and do
chmod +x IOTA.command
to make your running script executable. Hope this helps.