Standard mmorpg classing.

You have your 3 standard Types and then your subclasses branched off that.

Generally you go Type >> Race >> Class. Type is usually Tank, Damager and Healer then you add your racial subtypes that give bonuses towards each type and then choose your class after that. Your choice of Type and Race restricts your choice of Class.

In this case you have Ranged (stand back and shoot from a distance. Often combined as a support role), Tank (go head first in and soak up the damage, while dealing pretty good damage. These are the long haul fighters built for stamina), Healer (keeps everyone else in the game) and Force Lightning Damager (the aim is to take down your opponent as quickly as possible so you don't get hit).

Usually you want at least one of each, so the tank takes all the aggro, the healer keeps the tank alive, the support guy buffs everyone elses stats while damager rips into the enemy as fast as possible.

If you still don't understand any of that then you've obviously only ever played COD:MW type FPSs online, as it's been standard in any role playing game since the days of Gary Gygax.