Overlay pages appear in a pop-up layout that users can close to return back to the page they were previously on. They are best used for one-off directional or informational pages.
You would edit an Overlay page like a Standard page in a one column layout. The main difference in a overlay page is that there are no navigation options. Overlay pages also ask for a Manual Overlay Close Path. This path will be where a user is directed to after they close the overlay if they did not start on a previous page, but came to the overlay page directly.