Kid3 is an audio tagging application for tagging audiobook files with MP3 metadata required for file distribution.
You need to tag your files so your reader can find the files and read the titles on any device they are using to consume your book. Do not assume that your audiobook distributor will tag your files for you, even though they may. While most editing software will tag your files, oftentimes they are only adding a v2 tag, but some mp3 players still only use v1 tags. Kid3 will allow you to fine tune your tags and embed all tags to your file.