Rules Index
Player Core Chapter 8: Playing The Game Downtime Mode Shopping and Crafting

Item Crafting

Source Player Core pg. 434
You can spend downtime to use the Craft skill activity, making new items out of raw materials. Crafting can be an excellent way to refine the gear the party uses, including upgrading items and preparing ones you're likely to need on an upcoming quest.
Skill Downtime Activities
Chapter 4: Skills includes several downtime activities, which are summarized here.
Craft: Using the Crafting skill, you can create items from raw materials.
Create Forgery: You forge a document.
Earn Income: You earn money, typically using Crafting, Lore, or Performance.
Subsist: You find food and shelter in the wilderness or within a settlement.
Treat Disease: You spend time caring for a diseased creature in the hope of curing that creature.