What you do is you plan out your animation in layers. Once you have every frame in sequence in your layers.. you then create a new "frame" and then hide the top layer. Then make a new frame and hide the second layer. Then make a new frame and hide the third layer. The peeling away of layers creates the animation.
So have your layers like this:
TOP LAYER VISIBLE----- first frame
|
V
BOTTOM LAYER VISIBLE--- last frame in the animation
