First when you get in to the chamber of secrets and you have talked to thomas riddle the basilisk will come wait until it has gone into on the holes and walk into the sword which is to the left of you. The target the black diamond on the chest of the basilisk and press triangle, square or circle then with the analog stick move the charge to the diamond. Do this until the basilisk is defeat but be careful when you hit the basilisk it goes wild and stone starts to fall from the ceiling.