Each Character has a Vocation. Their Vocation specifies their Primary Attribute, Experience Modification, Hit Points, Saving Throws, Combat Ability, what Items, Weapons, and Armour they can use, and some have unique features.
The Vocations to choose from are Cleric, Fighter, or Mage.
A Character can only have one Vocation, with the following exceptions:
Humans can change Vocation but Mages cannot become Clerics and Clerics cannot become Mages.
To change Vocation they must have a score of 16 or better in the Primary Attribute of the Vocation they wish to change to.
Elves can change Vocation as described in the Elves Species section.