Open a crafting table
Place 8 cobblestone blocks in the outer slots of the 3×3 crafting grid
Leave the center slot empty
Take the furnace from the result slot
Place the furnace where you want the smelter to be
Add fuel such as coal, charcoal, wood, or lava bucket
Add ore, raw metal, sand, or other smeltable items to the top slot
Collect the output from the right slot when smelting is complete