When you select this container, you’ll see the videos you’ve already given URL locations for on YouTube or Vimeo.  You’ll need your video to be on one of those two sites to place it here.

You can select one if you’ve already placed it here in your video library, or you can place a new one, as here:

Clicking outside the video in the container, you’ll see the Video Settings box on the right.  Choose YouTube or Vimeo for where your video resides.  Then just copy/paste or type in the URL of the video location.  That’s all you have to do to place a video in its own container on your site.