Hi
It's fairly straightforward.
The clips will be on different tracks, each with an FX box. The clip on the upper track will overlay the clip on the lower track
On Track 2 (upper track) click the FX and add a Crop effect. You can keep the AR the same or make the crop any ratio you wish.
Monitor the result in the Sequence preview window. You should now see some of the lower video track.
Click the FX in the Track 1 (Lower) video and do the same.
You can move either of the cropped frames to another position by adding a Position effect to them and then dragging them to where you want.
Nat