If you have a server you should install PHP and MySQL as shown at this place http://docs.moodle.org/en/Installing_AMP
MAMP should be used only for a local installation so every Moodle beginner can work as an admin or as a trainer without the fear to kill a production installation. Please remember that MAMP has a lot of holes in its security system. There are prededined passwords in the package.
For MAMP security please look on
Please do not use MAMP as a server installation!