You've not told us which version of Windows you're using (or even if you're using Windows at all). The following works with Windows 7 and earlier:
Click on the Start button and then on All Programs.
Locate Google Earth in the list and right-click on it.
Select Send To > Desktop (Shortcut).
Job done!
If you're using Windows 8 you might need to create a tile instead of a conventional shortcut:
http://www.techrepublic.com/blog/windows-and-office/quick-tip-create-a-tile-on-the-windows-8-start-screen/