One shortcut many Windows XP users came to rely on was "Show Desktop" on the Quick Launch toolbar. You can see it in the top screenshot, outlined in yellow. The purpose of Show Desktop was to minimize all open windows, making the desktop background visible. In Windows 7, however, that icon doesn't exist anymore; what gives?
Show Desktop is still around in Windows 7, but it's been radically redesigned and moved. In fact, if you don't know it's there, it will be almost impossible to find. It looks like no icon at all, and is essentially hidden. Show Desktop is now a small rectangle all the way on the right side of the Taskbar. Notice in the graphic (the second image; click under the graphic to the right to find it) that the arrow points to it.
It also has more functionality now. Hover over the icon without clicking it, and you get an "Aero Peek" of the desktop; move your mouse off the icon, and the open windows are visible again. If you click the icon, all open windows are minimized, just as they were with the old Show Desktop icon under XP. Click it again, and it will return your open windows once more.