On Necronia, there are three vocations that branch out into 4 different classes each. You are able to get promoted once you finish the training course for your class on the Island of Judgement. You can get there by leaving Bawfuria using Captain Sharkslasher's boat.

Basic Vocations
Warriors are a vocation that excels in melee combat, using swords, axes, clubs or even their own fists.
Their spells revolve around their weapon and their skill, and have a little to do with magic (in most cases).
They get promoted into swordsmen, defenders, berserkers or wildhearts.
Rangers are a vocation that makes use of various utilities combined with a ranged weapon in order to take down their enemies as quick as possible. They can throw knives and shurikens, spears; fire crossbows, bows and even guns. They get promoted into spearmen, hunters, marksmen or shadowstrikers.
Mages are a vocation that heavily relies on the use of spells and mana for various purposes. Their magic can be used to revive the fallen, control the elements, summon minions, buff the party, and more... They get promoted into spellcasters, summoners, necromancers or saints.
Classes
Each vocation can promote into several different classes. Each of these classes further improves your character and makes it specialize in some disciplines, depending on the class. For example, if you promote from a warrior into a defender, you still get to beat things up with your club, but you also get new abilities that will help you fulfill your new role.

Click on an icon of a class to read more about it: