Craft or find a furnace
Place the furnace on the ground
Open the furnace
Put smeltable items in the top slot
Put fuel in the bottom slot
Wait for the item to smelt
Take the output from the right slot
Use coal, charcoal, wood, planks, lava buckets, or other valid fuel
Smelt ores, food, sand, clay, and other furnace-compatible items
Use a blast furnace for ores and a smoker for food if needed