In Windows the “show desktop” button is right at the bottom of your screen in the lower right, some users miss this function when they come to the Mac from Windows. The good news is that a “show desktop” function is there in OS X, it’s just a little hidden.
On your Mac keyboard simply press the fn and f11 keys at the same time. All of the windows on your screen will slide out of the way to reveal your desktop. And when you want the windows to come back you can simply press fn and f11 again and your windows and applications will come back.