On the level in Moria dubbed "21st Hall," the rest of the Fellowship will be fighting the two cave-trolls whilst you attempt to find an exit. Many people get boggled on this level. The trick to it is to move to the center, where the statue is, and push the blocks to their correct locations. After this, several rays of light will converge on the walls and the door will open, allowing you safe exit. Note: your magic or sword will have no effect on the trolls, so don't attack them. It'll only deplete your health.