How Do I Load An Mp3 Audio Book Into My Garmin 660? The Instructions Are Unclear To A New User.?

Plug your 660 into your computer via the usb cable. This will create a virtual drive on your computer. On my computer it is Drive L:, but this will vary based on the other drives you have on your computer. Open this drive. You should see a directory called “Audible”. Place your audio books in that directory. I don’t know if this requires that they be in Audible format (.aa) for them to show up. The other option would be to put them in the MP3 directory, and treat them like mp3 music files. It should allow you to play them, but the bookmarking, etc. probably won’t work.
If the file needs to be in you may be able to find a convert from MP3 to AA format. I found one at http://www.all-music-converter.com/ that might do the job.