How to tween using external images?

I just started Synfig. While looking at Skeleton tutorials, I read that bones had to be linked to handles. However, if I wanted to use pre-drawn parts I imported, how could I link bones to them? Would outlining them using the spline tool work, or do I absolutely need to draw parts within Synfig?

import the parts, create a hierarchy of layers, align them and add the skeleton
did you check Basic Bone Tutorial - Synfig Animation Studio ?

I checked, but I assumed those parts were drawn within synfig and had an outline already. I’ll try that, thanks.