Dexterity affects the damage of bows instead of strength. The bow is a faster weapon that uses arrows which are purchasable from the General Store located within each town of Flyff.
Bow users (in particular a Ranger) only requires Dexterity to increase their attacking power. They do not need to distribute their valuable stat points to any other unnecessary stat such as Intelligence. However not all builds are pure dexterity and more information can be found within the various class sections or guides within the forums themselves.
Click on the names of the bows below for more information and screenshots of them in game