The cradle is designed to hold the device in landscape mode with the connections on the back of the base section to allow the charger and a 3.5mm jack to be plugged in.
When the Tablet is placed in the cradle it will beep to indicate it has been connected (provided power is present) and will charge the battery. The 3.5mm jack socket allows you to connect the device to an external amplifier or other audio equipment but should NOT be used for headphone connections.
This smoked plastic cradle is designed specifically for the 8.9 tablet and will hold it securely allowing it to charge and be used/viewed (power required for charging).
On the rear of the base is a 30pin connector and a 3.5mm jack socket. The 30pin connector is used to charge the tablet when installed in the cradle and the 3.5mm socket allows you to connect to an amplifier or other audio device and listen to audio from it.