Arrows can be crafted from a variety of item drops.
The craftable items, and the number and type of arrows they produce can be viewed here:
http://www.pawdgame.com/database/arrowsTo craft arrows, use the "Arrow Crafting" skill.
To get such skill, complete the following quests from NPC Erik in Saliko Village:
- "A Deal With Erik"
- "Target Practice"
With the "Arrow Crafting" skill at hand, you will be able to produce arrows of every element type.
Though to start out, Bug Shells and Felixible Branches are good sources of arrows, specifically, Normal-Type.
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Note the arrow usage of skills:
-Auto Attack, Double Strafe, and Piercing will use a single arrow.
-Arrow Shower will use up a lot of arrows quickly, one for each enemy around you.
Considering how many arrows Hunters use, it's important to save up to purchase storage later on.
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I hope that clears things up!