Layer animation

Hello!
I'm currently working on a cut-out animation and I've run into a problem: I don't understand how to properly animate body parts so that they can move freely between layers.

For example, so that in one frame the hand is behind the body, and in the next - already in front of it. This is the example I'm aiming for.:
https://www.behance.net/gallery/192101547/The-Twelve-Chairs/modules/1117336699

I would be very grateful for any advice or ideas on how to implement this. Thanks in advance!