Download lets you sync your movies to your mobile device and watch the movies later without the need for an Internet connection.
It's really simple. Select the movie that you like, and you'll see the option to "Download”. Tap that, and select the quality of the video you’d like. Obviously, the better the quality, the larger the file size. Select the quality that you prefer, wait for it to sync fully, and that's it.
You can now enjoy your movies anywhere without any Internet connection.