This is direct from the manual. Hope it helps:
Transferring files from your PC
You will need the included USB A to Mini-B cable to do this:
1. Connect the cable to your PC and to the AirPad.
2. Hold the AirPad in a horizontal orientation. You will see a
USB symbol in the notification bar at the bottom right of
your AirPad’s screen.
3. Touch the USB symbol and drag it up to bring up the
notification menu.
4. Touch USB Connected.
5. In the window that appears, touch the Turn On USB storage
button.
Your AirPad will now appear as two different Removable Storage
Devices in “My Computer” on your PC - one for the main device
memory, and one for the MicroSD card.
Transfer files like you would transfer from any drive to another.
Once you are finished transferring files, follow these steps:
1. Click on the Safely Remove Hardware icon in your PC’s System
Tray, next to the clock. Click on Eject, or Safely Remove USB
Mass Storage Device.
2. On your AirPad, touch Turn off USB storage.