This video show how easy it can be to animate in DigiCel FlipBook.
You just draw a frame, go to the next frame and draw it.

FlipBook’s lightbox lets you see any image you want while you draw.

You can see several previous image, several future images and the relevant images from other layers as well. Being able to see what you want makes it easier to know right where to draw the current frame. It doesn’t get an easier than that. You see what you want and you draw what you want.