You can base them off DnD style classes, or by the people who are in that class listed by the wiki. For example we can assume Berserker is a damage oriented character, or a champion is a defense wall. Characters like Ki Masters have an inclination to project spiritual power in one form or another like Sebas using it to make stronger melee attacks, or project a debuff. In other words much like a monk which is also what he is.

Paladin tend to be heavy warriors who use minor mages to empower themselves, or to help allies with minor healings. While Templars seem to be healers who are also able to be full on combatants.