How to work furnaces in Minecraft?

Put wood, coal, charcoal, or a bucket of lava in the bottom, put raw food or ore in the top. It will fill up the fire icon in the center and start cooking. The right-facing arrow indicates cooking progress.

You can't heat water.

Coal/Charcoal/Lava is a much more efficient heat source than wood. If you need coal but don't have any, try putting a block of wood in the bottom and wooden planks in the top (or vise-versa, can't remember clearly). This will burn the wood and create charcoal that you can use to make torches or use as a better fuel source than wood.

You cook things by placing as many piecies of coal you want in one side of the box, while you place the object you want to cook on the other box. You can't heat water XD.

MINECRAFT SUCKS DON'T PLAY IT Please. ITS THE WORST GAME IN THE UNIVERSE ITS So RANSID ITS DISGUSTING I WOULD NEVER PLAY IT JUST DON't PLAY IT AND IT WON't RUIN YOUR LIFE.