Vulnerabilities, Resistances, and Immunities

If you have Vulnerability to a damage type, damage of that type is doubled against you. Vulnerability is applied only once to an instance of damage.
If you have Resistance to a damage type, damage of that type is halved against you (round down). Resistance is applied only once to an instance of damage.
If you have Immunity to a damage type or a condition, it doesn't affect you in any way.