CORRECTED** Thank you @
Dipstik-sportech for correcting me. These are the shims for the pinion. You use them to set the preload on the bearing. If it is not set correctly, it will either spin too freely or be more difficult to spin.
This is the shim I used for setting the pinion depth. It goes in between the pinion gear and the pinion bearing. This is the one that determines how far into the carrier the pinion goes.
It goes here
I don't have pictures of the shims for the differential, but what they do is position the differential and ring gear left to right to get make sure you get proper contact between the ring gear and pinion gear. Too far one way or the other and you either have too much contact or not enough.