There isn't that much in the Moon Labyrinth.  All you have to do here is to go up one place, go right one place, and then keep going up.  About 4 rooms up, go right to fight 3 Blue Goryias.  Be weary of the stone statues as they spit fire.  If you kill the Goryias, you will win the Magic Boomerang.  Return back to the room you came from and continue going north.

Three rooms later, you will fight Dogongo.  Carefully plant bombs -- two of them are needed to destroy Dogongo.  There is a trick if a bomb goes off and Dogongo gets hit, you can instantly hit him in the head (you must do this fast) and Dogongo will die.  Only use this trick if you're short on bombs, however.

After Dogongo is gone, the container heart appears and the west door will open for the Triforce fragment.  Claim the heart and then go through that west door.