Picture in picture creating

I'm not sure what this technique is called but hopefully you can see in the attached jpg. Basically, you have a video clip playing and then that clip is animated (moved) into the upper right corner of the screen as another video clip is played below or a still graphic appears center screen. I'm trying to ascertain what that technique is called and if anyone could please share a link to a good video (shorter the better) showing you how to re-create that technique I'd be very appreciative. Thank you.