Inputting M3U playlist URL allows you to watch live IPTV channels free, including movies and TV shows. An M3U player such as Kodi with IPTV free channels plugin activated and setup uses these to provide access to lots of streaming online video.
The M3U file itself is simply a text file containing a list of media (audio and video) file URLs. The media files can be MP3, AVI, M4A, MOV, and many more. Kodi reads this list then provides a menu for you to pick from. It will then play any streaming media file on the list for you.