You need to stand on the podium so that you are protected, wait to see the circle of light appear in one of the holes and perform the spell to raise the correct wall over the hole. When the basilisk breaks through the wall he will be dazed which allows you to struck at him with the normal spell. (sorry can't remember the names of the spells. Keep repeating this until you have done this for all 4 holes.
You will then move on to another section, keep running forwards and call the snake to you each time you see the green snake symbol and then raise the slabs to jump on. At times you will be blocked by the snake and will have to go backwards to call the basilisk to the lower holes.
When you get a bit higher you will be blocked by both the head and the tail, if you strike at the tail it will move. After all this you will find yourself ontop of the statue where you will break a box to find a sword, cast the spell to strike the basilisk with the sword and enjoy the story clip that follows.
Hope this helps