If you are looking to the Air Cleaner from your driver's side it is located to the right of the air inlet. Kind of hidden under the Throttle Body. You will recognise it because is connected on an elbow like rubber pipe and you should see Motorcraft on the valve it self (if it is stock).
If you still don't find it, post again. I can give you more detailed directions. I had a hard time finding it also, despite the good efforts of people on the board.