If it is what I think it is, you need a bowl, a fire and either malachite or cassiterite.
Step 1: Drop the bowl.
Step 2: Drop malachite/cassiterite.
Step 3: Pick up the item (Now you have a filled bowl).
Step 4: Drop wood near the fire.
Step 5: Drop the filled bowl while being near the fire .
Step 6: Press Action after the you see that the content of the bowl changes.
Step 7: You finished making either Copper or Tin.
I hope that helps! You should look into the guide, because it also explains it.