There are a few different ways you can download movies to your mobile phone:

1. Purchase or rent movies from an online video service like Google Play, Amazon Prime Video, or Netflix and download them to your phone.
2. Use a free movie download app (though keep in mind that many of these apps are not legal and may be risky to use).
3. Download movies from a website onto your computer, then transfer them to your phone using a USB cable or a file-transfer app.
4. If you have a DVD or Blu-ray movie that you want to watch on your phone, you can use a DVD ripper program to convert the movie to a digital format, then transfer it to your phone.

Some key instructions to follow before downloading a movie:

1. Make sure you have enough storage space on your phone to accommodate the movie file.
2. Check that the movie file is compatible with your phone's video player.
3. If you're downloading a movie from a website, be sure to only download from reputable sources to avoid downloading malware or viruses.
4. If you're using a free movie download app, be aware that many of these apps are not legal and may be risky to use. Some may contain malware, and downloading movies from these apps may infringe on copyright laws.
5. Consider the data usage involved in downloading a movie. If you're on a limited data plan, it may be more cost-effective to stream movies rather than download them.
6. If you're downloading a movie from a website or using a movie download app, be sure to read any user reviews or ratings to get an idea of the quality and reliability of the source.
7. If you're using a DVD ripper program to convert a DVD or Blu-ray movie to a digital format, make sure that you have the necessary permissions to do so. In some cases, this may be a violation of copyright laws.

Keep in mind that it is generally not legal to download copyrighted movies without permission from the copyright holder, and that doing so may be risky as it may expose your device to viruses or malware.