Furnace is a Functional Blocks item in Cube life: Survival Island that allows you melting ores and rocks together while also working as an oven to cook food. At least one piece of Coal is used to do anything on the Furnace, Charcoal may be used as well, but it requires 2-4 times the amount of coal to work.
To use a Furnace, press ZL on it to open it's interface. You have two crafting slots and one Coal slot. The amount of coal needed to perform actions depends on what you are doing such as smelting sand into Normal Glass requires one Coal up to smelting Titanium Ore which requires twelve Coal. For a full list of items you can create and their coal requirements, go to Furnace Crafting. The furnace can no longer be picked up and moved (v1.2) it will eventually break after a certain number of uses. Like the crafting table, make extras for a centralized storage location.