The metro screen is the start menu spilled across your desktop. That's the best way to think of it. Even if you are in the desktop mode, hovering where the start button used to be brings up the metro icon and clicking that puts you in the desktop.
If you want a start menu on the desktop side, simply right click the task bar and select Toolbars then New Toolbar. In the dialog that comes up, browse to...
and click Select Folder. Now you will have a task called Programs with a chevron. Click the chevron for your start menu.
Now you can safely clean up your Desktop and get back to work!