For each instance of damage the player inflicts on an enemy, the following calculation is applied:

Base DMG * Base DMG Multipler is usually calculated as a character’s ATK multiplied by the skill multiplier. In some cases, a skill may scale from other attributes such as HP, DEF, or Elemental Mastery instead of the typical ATK.
If the damage triggers a CRIT from CRIT RATE, the CRIT DMG multiplier will be applied:
