Draw a little. Turn the page. Draw it again, slightly moved.
The faint drawing underneath is the page before this one. That is the only trick in animation that matters at this scale — you are not drawing a picture, you are drawing the difference between two pictures. Turn it off if it gets in the way.
Every page is kept as the strokes you made rather than as an image, so the drawing stays crisp at any size, the thumbnails are the real pages, and undo can take back exactly one line. The whole book lives in this browser and is still here tomorrow.
Twelve pages a second is the usual working rate for hand-drawn animation on twos. Four is a flick-book on the corner of a school exercise book. Both are on the slider.