I think I understand what you're asking. If you're talking about making a layout where you start a new page, and you want to add different files to the "new" layout, here's what I do. Right click on the blue bar at the top of the element file you want to add, and click copy, or the keyboard command is ctrl+c then go to the "new" layout that you want to add it to. Make sure the blue bar at the top is highlighted by left clicking it. (If you left click the new layout, you can use ctrl+l as a keyboard command, and it will automatically paste itself as a new layer.) If you right click the mouse on the new backgrounds blue bar, there is a command that says paste as new layer. That will do the same thing. Whichever way works for you.
Wow-is your head spinning? Mine is! LOL! Hope this helps!
