In Setting Up a Basic Cron Job in Linux, I went over how cron jobs work and how to set one up.
Recently I wanted to set up a cron job on MAMP, and could not find any resources on how to get that done. I figured out that you need to call MAMP's PHP executable, which will depend on on the version of PHP you're running. For 5.6.32, the below would be the proper URL.
*/1 * * * * /Applications/MAMP/bin/php/php5.6.32/bin/php /Users/isfaaghyth/cron.php > /dev/null 2>&1
Just change the version number to whatever version of PHP MAMP is currently running.