Explain the basic rules for the riddle game

The rules are simple. If Gollum asks and Bilbo can't answer.... he gets to eat him. But if Bilbo asks, and Gollum can't answer.... Gollum has to show him the way out of the cave.

"Does it guess easy? It must have a competition with us, my preciouss! If precious asks, and it doesn't answer, we eats it, my preciousss. If it asks us, and we doesn't answer, then we does what it wants, eh? We shows it the way out, yes!"