Once you get that puppy plugged in, then you will need to set it up. See instructions here.
Then you will need to know how to play movies on your Apple TV from your iPhone. See the tutorial below:
I installed the NFL app on your iPhone. You should be able to apply what you learned from the tutorial above in a similar fashion. Turn on your Apple TV. Go to your iPhone and open the NFL app. Select the game you want to watch and then look for the airplay button (that you saw in the tutorial above) and hit that to flick it to the Apple TV.
Call me if any dramas!