A Throwing Knife is a ranged weapon (does not add damage to melee attacks), and is thrown like a shuriken. When thrown there is the same particle affect that applies to arrows.
The Throwing Knife is it's own ammo (like the Shuriken or Javelin), and the maximum amount of ammo it can hold depends on the material it is made of.
When it is crafted, it is at it's maximum Knife storage (depending on materials used. All Manyullyn will make more than stone and wood).
You can also add modifiers to it.(Note: The moss modifier slowly refills the amount of throwing knives back to it's original total, similar to arrows.)