Window>Tile Horizontally -- how to undo?

Once I tile several open documents/windows, how can I "untile" them?  I need to view across more than one then be able to work exclusively in one without closing the other/rest.  

I can cascade them but if I click the box to enlarge the window (in the upper right), my menu/command bars go away.

I need some guidance on how to maneuver with multiple windows open.

Thanks!!

Lisa in The Lowcountry