You put all four clips on to video tracks 1 through 4.
Put the clip you want in the upper left on track one, upper right on track two, bottom left on track 3 and bottom right on track 4. (These are arbitrary but follow these steps first, you can change things later.) You may wish to create a video track 4 in advance, or you can just drop the clip into the gray area above track 3 and it will create track 4 for you.
Select the clip on track one. Look in the Effects panel and apply the first preset under PiPs, 25% PiPs, 25% UL – named PiP 25% UL
Select the clip on track two. Apply the first preset under PiPs, 25% PiPs, 25% UR – named PiP 25% UR
Select the clip on track three. Apply the first preset under PiPs, 25% PiPs, 25% LL – named PiP 25% LL
Select the clip on track four. Apply the first preset under PiPs, 25% PiPs, 25% LR – named PiP 25% LR
That should do the trick. After you understand how to use the standard PiPs, you can use the presets that scale in and out and spin, etc.