Apple TV (1st generation) - Manual (Page 20)

20 Chapter 2 Configure.
Pairing with iTunes
After you set up your network connection, your TV screen displays a five-digit
passcode, which you’ll need to enter in iTunes to sync or stream content from your
computer to Apple TV.
To set up Apple TV with your iTunes library:
1 Open iTunes on your computer.
2 Select the Apple TV icon with “Click to set up” next to it in the Devices list.
3 Enter the 5-digit passcode from your TV screen.
After you enter your passcode, you can name your Apple TV and set up iTunes to
manage your content.
For more information about iTunes, open iTunes and choose Help > iTunes Help.