From Medivia Online Wiki

Dexterity is a stat only gotten through items, it increases your Distance Skill damage and Spellpower.
It can be used by archers and players with no vocation only.
The amount of dexterity you get from a certain item is directly related to its Item Rank.

One point of dexterity increases:
-minimum distance weapon damage by 0.80
-maximum distance weapon damage by 1.20
-spellpower by 0.75

Many equipment pieces and distance weapons provide Dexterity, often both as a Property and as a possible Attribute. Other items, such as the Green Witches Potion and Sweet Maris Feast temporarily increase your dexterity.