Instructions
Right-click any furnace in your home. A dialog box will appear, displaying three boxes: two on the right and one on the left.
Place a source of fuel in the bottom box on the right.
Place blocks of gold in the top box on the right. Wait a few seconds for the gold to smelt. When completed, a gold ingot will appear in the box on the left.
Drag the gold ingot into your inventory to complete the smelting process.