Load it
Drop ore into the hopper and it becomes ingots. Sand becomes glass, copper or iron scrap melts back into an ingot, and wood chars into coal. You can throw things in, too. Anything it cannot use is handed back with a clunk.
Keep it fed
It burns coal first, then wood. Iron and gold take longer than copper and burn more fuel. Rain cools an open smelter, so a roof over it keeps it working well.
Collect
Fresh ingots glow and steam as they cool on the tray. Take them from the tray or the bins with your hand. A full tray stops the smelter until you do.