There are many styles of gameplay within World Of Warcraft, depending on whether it's Horde or Alliance. But it all comes down to Class:
This particular role means that the player will be on the front of the battle, taking all of the damage to
protect their allies.
Classes within this role are: Druids, Paladins, Warriors, Death knights,Monks, Demon hunters.
When it comes to dungeons or even fighting against difficult bosses, it is key to have members that play a role that assist the tank as the tanks main focus is to take all of the damage whilst their team attacks. Classes that fall into this role are: Druids, Paladins, Warriors, Rogues, Mages, Shamans, Warlocks, Hunters, Priests Death knights, Monks, Demonhunters.
Healers play a leading role within World Of Warcraft, as without this particular class, the DPS and Tanks wouldn't be able to fight challenging bosses, meaning that players would continuously die within that area. Healers require a lot of focus. Classes that are able to be Healers are: Druids, Monks, Paladins, Priests, Shamans.