On the desktop it is as easy as right-clicking on the desktop and clicking new-link to application, then type the command that launches the app in the command field, or browse to it.
From the command line a symlink is created as such
ln -s <path to original> <link name>
For example to link firefox on my desktop I would type
ln -s /home/pcghost/firefox/firefox.bin /home/pcghost/Desktop/Firefox