To watch your movie, go to Store>Purchased in the left-hand menu bar of your iTunes window. Click on the downloaded movie title and press the "Play" button as you would to play an audio track. The movie will start playing in the "Now Playing" box in the bottom left corner. Double-click on this window and the movie will open in a separate window. To make it full screen, right click (PCs) or control+click (Macs) and select "Full Screen" from the list that appears to enter full screen mode. To exit full screen mode, press escape. You do not have to be connected to the internet to watch your movie.