I add the only user name I use as admin, click update, then nothing shows up on the desktop.
It will not "show up" on the desktop like a normal drive that is directly connected to your Mac, since it is a "network" drive when you connect it to a network USB port.
Click anywhere on the open desktop to display the Finder menus at the top of the screen
Click the Go menu, then click Network
Double Click on AirPort Extreme
The name of the drive will be displayed as a folder
You may need to click "Connect As" in the right hand side of the window to connect the first time that you do this
Double click the folder representing the drive to mount it on the desktop
Or, you can do the same thing by opening any Finder window
Look for the AirPort Extreme under the SHARED heading on the left
Click the AirPort Extreme to display the folder representing the drive, etc.