Instructions
Tap the furnace to open an inventory menu that contains all of your smeltable and cookable items.
Touch the item you want to melt down or cook, as well as a fuel source. They will appear in the appropriate boxes and show you a picture of the resulting item in the output box.
Watch the gauge on the arrow next to the output box to keep track of the melting/cooking progress. It takes approximately 10 seconds for the process to complete.
Tap the output box to put the newly created item into your inventory. Click the "X" in the corner of the window to close the furnace screen.