STEPS to create an animation by using onion skin are as follow :–
open a new file.
draw a bird or any type of drawing u like.
select the onion skin button.
right click on frame button and select insert keyframe option from the context menu.
choose the selection tool and double click on the bird or on the drawing.
move the drawing slightly.
click on the stage to deselect the bird.
click on frame 3 and press f6 to insert keyframe.
to stop the movement select control>stop option.