When you become a specific class, you start with nothing. No training, no skills, no spells. You are basically saying this is what you want to be. After you decide, you must go on quests and travel around to study the specific things relevant to your class.
Note: These are not the only classes that will be found in this world. There are quite a few other hidden classes that some people may fall upon through their travels. Please don't ask for them or ask for hints.

White Mage
White mages draw on the divine magic to heal and protect themselves and those around them.

Black Mage
Through devastating magic spells, Black Mages bring tremendous firepower to the battlefield. A Black Mage's job is simply to cast offensive spells and destroy enemies.

Warrior
Specializing in the arts of battle, Warriors are masters of all aspects of melee combat.
Warriors are a very versatile melee class that can equip almost all of the armor and weapons available.

Monk
With their bodies that double as deadly weapons, monks attack enemies with explosive strength. Monk is designed as a Hand-to-Hand weapon specialist, and is capable of wreaking havok with fast and furious punches. Monks are a force to be reckoned with on the battlefield.