The Add Frame-Content Overlay dialog box enables you to add frame-content overlay (FCO) in the current frame. You can add as many FCOs to a frame as you like. Each one will be another layer displayed inside that frame. The different FCOs are displayed to the viewer when the viewer clicks on the corresponding links.

There are two options:

Create New Resource tab

New frame-content overlay in the frame can be created by creating a new blank physical resource in the physical structure of the site.
Select page (resource) type from the displayed types:

Use Existing Resource tab

If you have previously created physical resources in your web project, you may use it instead of adding a new one. The resource can be used in many Frame Sets at the same time.
The window will display the list of page and image physical resources you currently have in your project. Select the one you want and click OK.

To delete a Frame Content Overlay, click inside the frame where the overlay is, and from the Frame Content overlay pull down box, select the FCO you want to delete. From the main menu select Frame > Delete.
For details refer to Frame Manager.