There should be a URL displayed on the bottom left corner of the screen where it says "Visit". Type this into your internet browser.
If you do not already have the AirMedia client installed, you will be prompted to do so.
Open the AirMedia client.
Enter the address from the bottom left corner of the screen again.
Enter the code from the bottom left corner of the screen.
Your laptop screen will now also be shown on the large screen display.
Volume can be controlled via the AirMedia client on your laptop or from the physical control panel.