Mages are the mighty brains of this world. Mages in Ancient Anguish, once they attain the tenth level of experience, can choose to enter a specialized school of magic. Transmuters study the art of changing and mutating objects.
Conjurers study the art of calling things into existence.
Invokers study the art of initiating natural actions. You can join and leave schools at the Tower. Leaving a school causes you to forget some of the spells from that school. These study hours are based upon your stats and experience, and will increase as you advance. You can then spend these study hours on spells, using the 'study' command in the mage hall.