Hi EDLIU,
Welcome to the Support Communities! I'm including some information below for you that explains how to use Apple TV. The HDMI port needs to be on your television, not your computer. The Apple TV connects to the TV with an HDMI cable. Communication between the Apple TV and your computer, iPhone, iPad or iPod touch takes place over your wireless network.
Apple TV - Apple Store (U.S.)
http://store.apple.com/us/buy-appletv/appletv
Apple TV gives you access to the best 1080p HD content — including blockbuster movies, hit TV shows, live sports, your music, photos, videos, and more — right on your widescreen TV. You can even play content from your iOS device or Mac on your TV using AirPlay. Apple TV requires an HDMI cable (sold separately).
Just plug in the power cord and connect Apple TV to your HDTV with a single HDMI cable (sold separately). If you have an iPhone or iPad, hold it near Apple TV, and Apple TV will learn about your home network and receive your iTunes account settings automatically.7
Apple TV - Apple Support
http://www.apple.com/support/appletv/
Cheers,
- Judy