Damage has a type, such as acid, bludgeoning, cold, fire, force, lightning, necrotic, piercing, poison, psychic, radiant, slashing, or thunder.
Resistance. If a creature or object has resistance to a damage type, damage of that type is halved against it.
Vulnerability. If a creature or object has vulnerability to a damage type, damage of that type is doubled against it.
Immunity. If a creature or object has immunity to a damage type, damage of that type is reduced to 0.
Apply resistance and vulnerability after all other modifiers to damage.