Put the two clips, one above the other, on different tracks and then select each in turn and use 'Effects' tab >> 'Movement effects' >> 'Size/Position'. Your Help menu has more detail under 'Size/Position.
Or even simpler if you want to see all of each clip (with black at top and bottom) - with clips one above the other on the timeline / arranger:-
Go to "Effects tab > Design Elements > Picture in Picture" and drag the first PinP in the folder "2/1 Left" onto one clip and the next "2/1 Right onto the other clip. You can then modify if you wish by using the "size / postion" effect by dragging in the preview monitor or editing the dimensions in the boxes.
Tip > to drag something larger than or outside the preview screen > click the 100% Down Arrow at the bottom of the monitor and reduce the viewable area to 75 or 50% of the window.