The smelter is a crafting type building in Valheim that let's you turn ores into ingots. This is an early game building that can be unlocked after obtaining a surtling core and a stone. You can only place the smelter near a workbench anywhere in the radius the same as building a wall or any normal building placement.
The smelter allows you to smelt the following ores:
In order to smelt ingots you'll also need coal, which can be obtained from a charcoal kiln. Alternatively you can let food sit too long over an open fire which will burn it into coal. It takes 2 coal for each ingot that you want to produce. Ores take 30 seconds of burn time to smelt.
To build a Smelter you'll need:
Once you have the ingredients you can place the smelter with the hammer tool. Right click (default key) with the hammer equipped to bring up the building menu, then select the crafting tab. Once you've found one surtling core and one stone it will be unlocked in your crafting tab.