Assuming you have Go installed, run go install github.com/beauxarts/binder@latest and you'll get binder binary in your $GOPATH/bin.
Run the following command:
binder pack-audiobook -directory PATH-TO-DIRECTORY-WITH-MP3S -title BOOK-TITLE -author BOOK-AUTHOR -cover PATH-TO-COVER-FILENAMEPacking an audiobook requires ffmpeg to bind individual audio files into a single .mp4 file. Optionally, if cover image is provided, mp4art (included in the mp4v2 tools) is needed. In most cases you don't need to specify the path to those binaries, however you can with the ffmpeg-cmd and mp4art-cmd parameters.