In the main series games, there is a concept of STAB (same type attack bonus), where a pokemon of a certain type will get an additional attack bonus (+50%) when using a move that has the same type. This bonus is in addition to any modifiers caused by the target pokemon's resistances.
For example, a Fire type pokemon using a Fire type move would do additional damage, compared to a non-Fire type pokemon using a Fire attack, or a Fire type using a non-Fire type attack.