Dan's Crypt is a mini-level to get you used to the controls in the game. The level is essentially two corridors making an "L"-shape. One of the legs has a Chaos Rune in it and the other has a life bottle and a Chaos Rune Hand.
Collect the rune, put it in the hand and go through to the end of the level. Make sure to collect the sword in this level, through it's almost impossible to miss.