With Picture in Picture, you can use FaceTime or watch a video while you use other apps.

When using FaceTime or watching a video, tap or press the Home button (on an iPad with a Home button).
The video window scales down to a corner of your screen so you can see the Home Screen and open other apps. With the video window showing, you can do any of the following:
Resize the video window: To make the small video window larger, pinch open. To shrink it again, pinch closed.
Show and hide controls: Tap the video window.
Move the video window: Drag it to a different corner of the screen.
Hide the video window: Drag it off the left or right edge of the screen.
Close the video window: Tap
.
Return to a full FaceTime or video screen: Tap
in the small video window.