Summarize:

Some subscription based services, such as Netflix, charge a monthly fee to let you to stream movies instantly as well as download them to your computer so you can watch them offline. Other services, such as iTunes and Google Play, offer movies that you can purchase and download individually with no monthly fee. And some services, such as Amazon Video, offer both options. Some of the popular on-demand movie services are:  iTunes Store (requires the iTunes app for desktop or the iTunes Store app for mobile) Google Play Store: https://play.google.com  Netflix: https://www.netflix.com/browse  Amazon Prime Video: https://www.amazon.com/gp/video/getstarted  YouTube: https://www.youtube.com Once you've decided which on-demand service you want to use, go to their website in a web browser or download the corresponding app on your smartphone. Most movie sources require you to have an account before you can access their content.  Many streaming services offer free trials when you sign up but will eventually require paid subscriptions. YouTube does not require an account, but if you sign up for YouTube Red, its premium streaming service, you're able to download content without hassle. With YouTube, you can watch many streaming movies for free but downloading requires either a subscription to Red or a workaround.  Not all streaming content is available for download:  How to check availability for download from Netlfix How to check availability for download from Amazon Many movies are available in both standard (SD) and high (HD) definition formats. HD movies tend to be more expensive and will use more room on your device. Apple iTunes, Google Play, Amazon, and CinemaNow offer movies for both purchase and rental.  Rental pricing and terms vary by source. Compare pricing among the different sources to make sure you're getting the best deal. Rental movies are removed from your device or disabled at the end of the rental period. You can watch most movies from most services on your desktop computer immediately. To get them to your mobile device, you'll usually need the proprietary app available from the Apple App Store, the Google Play Store, or the Amazon App Store. To watch on your TV, you may want or need additional equipment such as AppleTV, Google Chromecast, Amazon FireTV, Roku, or a smart TV.
Choose an on-demand service to fit your needs. Go to the service's website or open the app on your smartphone. Sign in or create an account when prompted. Browse the movie content and select the movie you want to download. Check to see if it's available for download. Select the movie quality. Decide whether to rent or buy the movie. Download the movie.