Because an M3U is just a text file, it is not possible to convert it to any media format such as MP3 or MP4; however, we can convert it to other playlist formats such as HTML or M3U8. This can be done by using certain applications like VLC or with the free Playlist Creator. Moreover, you can also convert the file to text if you wish to open it on a text editor.
On the other hand, M3U files are usually not made and saved from scratch. In a media player, you can use the options in the settings to save the currently playing songs to a playlist. Your M3U playlist may either consist of a relative path to the file or an absolute path. However, the advantage of using a relative path over an absolute path, is that the files could be moved to a new location or even a new device without having to maintain the functionality by making adjustments. Additionally, you may also refer to one M3U file from within another, but some media players may not support this.