I am not sure if its the same principal for overlays in all programs.

If I have a motion graphic, which is a book opening its pages. The page it opens to is black. How do I utilise this black to have another picture or video inside it. I want the page to open as normal and reveal the video clip behind.

I know its to do with overlays being in a certain order ie.... video track 1, 2 3 or 3 2 1 not sure. but not sure how to do exactly.