The class system for Ragnaros is called the formation system.
You see, each individual player starts with 3 classes at the beginning of the game and later can learn all six of the classes in Ragnaros.
The classes are:
Aggressor-Their main purpose is to physically attack the enemies.
Safeguard- Their main purpose is to defend allies.
Bulwark- Their main purpose is to strengthen allies.
Attenuate- Their main purpose is to weaken the enemy.
Alleviator- Their main purpose is to heal allies.
Liquidator- Their main purpose is to use magic to destroy the enemies.
The party will decide before battle what they wish for their battle formations to be. For instance if they want to have an Aggressor for physical attacks, a Liquidator for magic attacks, and an Attenuate to debilitate the enemy.
Also depending on what formation the parties have chosen, certain stat bonuses will be allowed depending on the formation. For example a party of all safeguards will dramatically increase the overall all defense of the party.
Parties are allowed to change their battle formation, but only at the beginning of the parties turn is this allowed.