Materials such as tin, copper and silver can be smelted directly.

Ordinarially; this is done in a furnace. With "Hardcore Furnace" Active. you are unable to create a regular furnace.

To smelt items, you need to make a large furnace(see recipes there). these are expensive and can not be obtained early game.

Before you have a furnace. you need to use a bloomery and manually create ingots, this is slow and tedious. It is best to save up and build a bronze furnace as soon as you can.