1. Zip the audio file
You should have audio title.zip
2.Add zip to Calibre by clicking add book Add tag such as audiobooks
3.Create new author virtual library . Name it audiobooks
4To make cover google or generate generic cover.
5.To play click on path. This will bring up file site.Click on zip to open MP3 files.
Of course you must have a program on pc to listen to MP3