Cascade: Choosing the Cascade command will arrange your windows in a cascading or descending fashion with the "active" Web page (the one you are working on) in front.
Tile: Choose Tile and any open Web pages you are working on will "tile". This is a nice way to see all of your pages at the same time.
Page Number or Name: This will list any pages open in Web Studio. Clicking on the name of one will activate that page. The check mark will signify which window is currently open.