If you wish to turn on your favourite screensaver into a desktop backgroup,please follw the steps.
Step 1
Right-click on the desktop and click on the Change Desktop Background option.
STep 2
select the Screen Saver tab.
Step 3
select the screen saver which you want to set as your new desktop background.
Step 4
close the Desktop & Screen Saver window.
Step 5
Go to Application folder > Utilities > Open Terminal Window.
Step 6
In the terminal window, Copy, paste and execute the following Terminal command which is shown below:
/System/Library/Frameworks/ScreenSaver.framework/Resources/ScreenSaverEngine.app/Contents/MacOS/ScreenSaverEngine -background
After entering the program in the terminal window,just minimize the terminal window.