Get a high-speed Internet connection if you do not already have one. Dial-up connections do not offer enough bandwidth for online streaming. A broadband connection is needed, though this service might be unavailable in many rural and geographically remote locations.
Buy a personal computer if you don't own one already. Most methods of watching movies online require the use of a computer, with a few exceptions.
Subscribe to Netflix. For as little as $8.99 a month for a subscription to their "one DVD at a time, unlimited DVDs per month" plan, you can watch as many of the movies they have available as you like. The online movies can be accessed on the Netflix webpage by logging into your account and going to the "Watch Instantly" section.
Use an on-demand video service such as Blockbuster On Demand or Amazon On Demand. These services charge a rental fee per movie as opposed to Netflix's flat subscription fee, but they have new releases available online. Netflix's online library has fewer new titles, making these on-demand services a good option for viewers who prefer to watch new releases.
Watch movies on Hulu. In addition to popular TV shows, Hulu also has many full-length movies available for online streaming. Like the rest of the content on Hulu, these movies contain short commercials but are free to watch.
Watch public domain movies online. Many movies have entered the public domain, making them free to show and to view. There are websites dedicated to public domain movies, and in fact many public domain movies can be found on popular video sites such as YouTube.