The goal in nethack is to retrieve the Amulet of Yendor and deliver it to your god. Doing so promotes you into the ranks of the demigods. However, there's always some catch, and there are quite a few here. There's a nasty Wizard of Yendor guarding the amulet, and you'll have to kill him, and he doesn't stay dead so you'll have to kill him over and over. Also, the amulet doesn't really like ascending staircases; sometimes attempting to do so with the amulet will magically take you down a bit instead.