It's a bit easier in Premiere Pro:
First off, go to the effects panel.
If you want two full frame images side by side, reduce the scale to around 49% and alter the "position" setting to get the clip where you want it
Alternatively, if you want to crop an image, drop the crop video effect onto the clip on the timeline, and then adjust the settings of the crop effect in the effects control
Now drop a clip onto a track above your first clip and repeat above.