Healer Class Heroes are supporters. All have ranged attacks and either heal Hit Points or refill the energy bar.
Mage Class Heroes have powerful skills. They tend to have ranged attacks.
Physical Class Heroes are your damage dealers. They tend to have a higher attack and attack speed than other classes.
Sacrifice Class Heroes can only be used to increase the skill level of other Heroes.
Tank Class Heroes are supposed to absorb damage. They tend to have more hitpoints along with lower attack and attack speed than other classes.