It depends on what you want to do. Warriors are melee attack close range. You can get elemental damage by gloves, but don't have any to start out with. As a warrior you can have two roles one being dps aka damage. You role there would be to get damage on the boss and adds in a dungeon. The other is tank which keep argo to prevent it from killing others like the dps or healer. As a warrior you have a skill called smite which I'd used to prevent skills some can kill if they go through.
Priest have two roles also one being healer. Your main goal is to make sure everyone stays alive by healing, revitalizing, emerald shield and more. The other is dps there a few routes you can go wind, poison, light, and dark. For the most part you are ranged damage. The only skill that I don't think is not is poison. You also have buffs you can buff your team with. This is mostly used as a other skill set. Another role is nightfalling your enemies. This makes the enemy sleep for a time, but will stopped if damage is done. You have two skills that do aoe one being poison dust and another exorcism(I think that's the name not sure it's not common as it only works on dark and ghost types)
Lastly is mage they are only dps and are ranged. The thing with them there are quite a few routes of elemental damage that can be done. Wind, fire, water and earth (least common to my knowledge). Like warriors you have a skill that can stopped a skill going through I think disrupt or dispell. I don't play often so I not quite sure which. As a mage you can use aoe which is a spell that has a big area of effect. You also have a skill that uses you mana as shirld. And some movement skills like skip (skips you a distance forward) and invisible (makes you in see for a limit time). You also have buffs skill that can be used called Arcane might
