You light a furnace in minecraft pe the same way you would in the PC edition. Once you have placed the furnace in your desired location you need to tap on it. Then when the screen appears you tap on the bottom box. Put coal/anything wood in. Then tap the top box and put what you want to cook/smelt in and wait for it to finish. Viola.
To access a furnace in minecraft, simply click it!!!! Its that easy!!
Press E. It should leave the furnace GUI.
You can't...
How do I light pilot light on furnace
You automatically get 1
yes
Burn cactus in a furnace.
Smelt Cobblestone in your furnace.
You put sand in a furnace
Shift while you place it.
You put cobblestone in a furnace with something to cook it with
You can't.