Core rule
Damage types
Damage types tell you which of the target’s resistances and vulnerabilities matter.
Bludgeoning, Piercing, and Slashing are physical damage types. Others include Acid, Cold, Fire, Force, Lightning, Necrotic, Poison, Psychic, Radiant, and Thunder.
One attack can deal both Piercing and Fire damage. Fire resistance applies to the Fire component of that attack.