Just click one of the buttons that says "free", and the movie is yours forever.
You can watch them on your computer, tablet, Roku, or smart TV with the Amazon Video streaming video app.
Always buy the HD quality if the price is the same as the SD quality.
HD movies will play in HD on compatible screens, and will also play in lower quality on non-HD screens.
However if you buy a SD movie, it could play in low quality on a HD screen.