How to add an icon to my iPad

Okay, I believe with Facebook icon, you mean a bookmark to Facebook (through Safari) and by desktop, you mean the main screen. If that is the case:

Open Safari, go to www.facebook.com

While the site is open, click on the share button (4th button on the top) on safari and select Add to Home Screen. As name enter 'Facebook', then you should have a Facebook icon on your home screen.

If this was the case, you should also give it a try to the new Facebook app. Go to app store, search and download it. It is free.

If you mean something else, let me know.

What do you mean by 'adding an icon'? Add the icon where? Some details please...

Go to the App Store, search for "Facebook" and select from the list of Apps and download the Facebook App. This will create a new icon on the iPad.

Yes, the app is completely free.

No worries, let us know if you are stuck at some point.