A few options. If F11 by default decreases volume for you, you need to instead press Fn-F11. You can change that setting in the Keyboard System Preference: Use all F1, F2, etc. keys as standard function keys . After enabling that, F11 will show desktop, and Fn-F11 will decrease volume.
If it's a new MacBook Pro, you can also use a 4-finger swipe up to show the desktop. Check out Trackpad in the System Preferences for a demonstration of that.
Also, in the Exposé System Preference, you can set up an Active Screen Corner where you can send the mouse to to show the desktop.
What others are referring to as Apple-H or Cmd-H refers to the ⌘H on your keyboard. That hides the current application and shows whatever's behind it, which may or may not be the desktop depending on what other applications are running. Switch to the Finder, close any Finder windows, and ⌥⌘H will hide all other applications, revealing the desktop. This would not show the edges of other windows.
Some people have mentioned that ⌘F3 also works to show the desktop. Learned something new!