3 Candles? Are you talking about the three pentagrams on level 1 of the catacombs? if so here is what you need to do.
Next to three pentagrams you should will find a manuscript. If you read the manuscript you'll discover you need to put the three magic orbs in each of the three pentagrams to open up a portal to the secret chamber. To do that, just drag each orb from your inventory to the center of each of the three pentagrams (the orbs will be in the "spells and scrolls" part of your inventory). If you place the orb correctly, it should start levitating. Once the portal appears and you use it to enter the secret chamber, the locked door will unlock, giving you easier access.
Good Luck and Fun Gamin.
J.W.