Most enemies are generally weak to a certain combat style, usually following the Combat Triangle Formula of Melee > Range > Mage > Melee. If your damage type is strong against the enemy, you get +4 to hit. If they are using the same style as you or have no weakness, you get no bonuses or negatives. If they are using the style that you are weak against, they get +4 to their Armor Class against you. You do not do additional damage for these weaknesses. The easiest way is to use an example. For this, we will assume you are using Melee.
Strong Against: Ranged
Neutral Against: Melee/No Weakness
Weak Against: Magic
Damage: