If I was using an LCD projector the projector needs to have an HDMI slot, or you need an adaptor. Kanex makes an HDMI to VGA adaptor. It is available on amazon.
Middle button on remote hold it down. This is your on off button.
You will want to get the Apple TV connected to the network.
Be careful about doing this around students, they will be able to see you put in the password.
Note: Your devices need to be on the same network as the Apple TV.
New to do an update.
If you want to connect to your computer you will want a newer (2009+) MAC running Mountain Lion. There should be an airplay icon along the top.
If you have a PC or older MAC you can use Air Parrot to mirror your desktop.
To connect to your iPad2 or new iPad or iPhone double tap the home button to start multi-tasking. Your recent apps will display at the bottom. Swipe the icons to the right until you see the icon. Tap this icon. Enable AirPlay mirroring. Note that you will have to tap this icon twice. Once to enable AirPlay and then again to switch the slider to turn ON mirroring.
When mirroring you may want to double tap and swipe once the icons on the bottom. Notice to the left of the play icons is a rectangle with a round arrow. Tapping on this locks your screen orientation.
Apple TV Articles you may enjoy
Untethered Teachers: Using Apple TV in the classroom
Kanex ATV connects Apple TV to VGA projectors
How to get AirPlay working when Apple TV is hooked up via ethernet
How to set up an Apple TV
Apple TV: How to use AirPlay mirroring
Thank you to Jon Corippo for sharing his Apple TV wisdom with me. You can view his slides from ISTE at http://rockstarteacher.us