Grey animated box in titles

Hi everyone, thanks alot for your help on this:

In some title templates there are animated grey boxes, that contain a arrow. I can click the box and distort the outline etc. looks like a place holder to fill in an image.
How do i use that? I dint understand how to place some content in here.

Cheers for your advice!
Andre

It is called a Drop Zone and you fill it by clicking on it in the Inspector and then selecting a photo or video clip to fill it with.
larryjordan.com/articles/fcp-x-drop-zones/