Mask Effect

-You name your first layer masked then click to 40 and insert a keyframe
-Then you add a new layer, and name it mask
-You also click on the 40 and insert a keyframe
-Then on your masked layer you draw what you desire wheather its shapes or anything you want
-You then create a shape that is bigger than your image
-On your mask layer go to modify timeline and layer properties click on mask and lock it
-Then you insert a motion tween and on the mask layer move your object or shape you made to go across what you just drew.
-As soon as you see the green line then thats where you know where the shape is going to be.
-Then you click on the masked layer and go to modify, timeline and layer properties then click on the masked and lock it.
-Then go to control and test your movie you are now finished and save your work.