If you have a Desktop cluttered with icons and wish to temporarily hide them from view, you can do so with a Terminal command.
To hide Desktop icons use:
defaults write com.apple.finder CreateDesktop -bool false && killall Finder
To redisplay Desktop icons use:
defaults write com.apple.finder CreateDesktop -bool true && killall Finder
If you prefer not to mess around with the Terminal, there are apps that can accomplish the same thing. The most popular one that I am aware of is called Camouflage by Bricksoftware. Camouflage sits in your menu bar and is easily accessible when you want hide your desktop icons. You can also configure a HotKey to show and hide your icons.