There are following ways how crafting may work:
1. make a new item with demanded bonuses
2. add demanded bonuses to existing item
Both ways may be done by some NPCs or by hero.
When done by NPCs, it may be unavailable at some times (because you may be too far from NPC that makes it) and expensive but without chance of failure.
When done by hero, it may be cheap (if you don't count price of demanded materials) and available at any time but with chance of failure.