This is a device that, when running, selects a random block to push out (There are 9 possible blocks: stone, netherbrick, glowstone, endstone, redstone, lapis, iron, diamond, or black wool, which represents that you lose). Once the block is pushed out, you can either push the button on the left to try again for a better block (Watch out, though, you might get a worse block, or black wool), or you can push the button on the right to accept your prize, in which case the corresponding item falls from the ceiling and the machine turns off.

The game starts by placing a sponge block in the netherbrick hole on the right side of the room and pushing the button. If you place your sponge in on accident, or decide that you don't want to play, then you can simply break the sponge. There's a 90% chance that it'll be safely returned to you through the water canal below.

If you place any block that can be pushed by a piston in the machine, other than a sponge, then it'll be taken and the game won't start. Sucks for you if you place you diamond block in and push the button. I warned you :D

If you put in anything that can't be pushed by a piston, well, nothing happens.