What happens next in this paragraph?

How to add personal movies to itunes
Check the format of the movie file you want to add.
Itunes only supports the mp4 (m4v) and mov formats. It does not support many popular formats, including avi, mkv, and wmv.
If your video files are not the proper format, you won't be able to add them to your itunes library. Check your video's format before proceeding.