OP, are you asking about the Airplay feature where you can mirror what is on the iPad or iPhone 4S or computer on your Apple TV?? If so, go to the Apple TV menus, go to Settings, go to Airplay and click to turn it on. Then go to your iPad 2, double click the home button and scroll left. You will see a triangle within a square. Click that and change from iPad 2 to ATV. Now you can play whatever you like on your iPad and show it on your Apple TV.
Airplay Demo
YOU DO NOT HAVE TO JAILBREAK ANYTHING TO DO THIS.
If you want to share movies/songs/whatever from your computer to your ATV, you must turn on sharing on the computer so the ATV can "see" your iTunes library.
Hope this helps