It sounds like you would like to AirPlay content from your MacBook Air to your Apple TV. I found some articles that have steps to help you set this up.
If you are running Mountain Lion (Mac OS X 10.8) on your MacBook Air, you can use the steps in the following article to setup AirPlay mirroring. AirPlay Mirroring lets you send what’s on your Mac screen to an HDTV wirelessly with Apple TV:
If you would like to AirPlay content from iTunes and not your full screen, you can follow the steps in the section titled "Enabling AirPlay from iTunes on your computer" in this article:
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