Every mob type in New World is weak or strong against certain damage types in the game. The below chart outlines which damage type does more or less damage to each mob type. You can slot gems into your weapons that have an available gem slot to obtain the desired damage type.
When damaging a mob, an icon will show next to the damage value. If there are small arrows above the icon, it means the mob is vulnerable to that damage type and your damage output will be increased. If there are two small arrows below the icon, it means the mob is resistant to that damage type and your damage will be reduced.
Your overall damage output is determined by your attribute points and your weapon damage. Gems scale off of particular attributes or weapon damage, whichever is higher. It's important to note that some of the increased damage types do more damage than others. The chart below also indicates the best and worst damage types vs each enemy category.