How do animators draw graphics at same place in each frame?
There may be a number of techniques used: 
Traditional animations had a complex workflow involving hand-coloured xerographed outlines. Backgrounds were drawn separately and reused (even in multiple films), and individual frames weren't all drawn by the same people.

A quote from the first link is instructive:


  A peg bar is an animation tool used in traditional (cel) animation to keep the drawings in place. The pins in the peg bar match the holes in the paper. It is attached to the animation desk or light table, depending on which is being used. 


A hand-made flipbook could just use a makeshift lightbox with a master outline fixed under individual pages held on pegs or even taped into a precise position.

(All links wikipedia, the first in particular is an interesting read)