There are several ways to quickly show and access the desktop.
1. Press the Win+Spacebar keys. Let up on the spacebar but hold the Windows key down. When you let up on the Windows key, you will return to the previous open application.
2. Next to where the time and date are shown on the system tray, there is a small rectangular box. Clicking on this once will show the desktop. Clicking on it again will return you to your previous open application.