Gathering brings in the raw goods. Refining makes the common materials from them, and refining a common one again with an additive makes the uncommon ones. Production takes them from there.
Common metal, refined from Iron Ore by Smelting at level 1 (recipe).
One Iron Ingot takes 4 Iron Ore and 1 Chunk of Coal.
Uncommon versions: Meteoric Iron Ingot and White Iron Ingot
Refined further into:
Production takes it, or its forms, in 78 Blacksmithing, 1 Alchemy, and 4 Carpentry recipes.
What it adds to gear parts made from it: