OK, you had me confused there. That's the Start Screen in your screenshot whereas in the heading for your thread you mention the Desktop.
By default, Windows 8 only allow you to pin certain file types (like exe files) and folders to the Start Screen. However, there's a registry hack that's describe in this article that will allow you to pin any file to the Start Screen. As usual, you should always exercise care and back up the Registry whenever you make changes to it.
OK, I have re-read your first post and I see you have installed MS Office and you want to have tiles for it on your Start Screen. I don't use MS Office but I'll try to explain how to pin a tile to the Start Screen for any program you install. Also, I'm on Windows 8.1 Update so if you are on Windows 8 you may find the screenshots a bit different but not too much.
1. If you are on the Desktop, go to the Start Screen by clicking the Start icon in the bottom left corner of your screen.
2. On the Start Screen, click the arrow in a circle near the bottom left corner. This will take you to the Apps View.
3. In the Apps View, scroll left or right until you see the App you wish to pin to the Start Screen. (Note: I don't use MS Office so I will use another App as an example).
4. When you find the App, right-click it and from the Context Menu click "Pin to Start".
And that's it! A new tile for the App will be pinned to the Start Screen. You can drag the new tile to any position you like or resize it.
Edited by Agouti, 18 October 2014 - 12:03 PM.