how to download mp3 book to iTunes

Good Afternoon 1Knute,

I'm not clear from your post if you are trying to add an audiobook in MP3 format or a disc full of MP3 music to your iTunes library.

If you are adding music ... you can insert the CD or DVD with the data files into your iMac, select all of the files using the Finder application and drag them to the iTunes icon on your Dock.

Or, you can create a folder on your iMac and copy the files from the CD or DVD into the folder, then add the folder to your iTunes library.

Add music to iTunes - Apple Support
https://support.apple.com/en-us/HT201169

If it is an audiobook that you have in MP3 format, I would suggest copying it to a folder on your computer first, and naming the individual chapters so that they are in sequential order. Then add the folder to the iTunes Library and create a playlist for the audiobook in iTunes.

Using the new iTunes - Apple Support

Get Info

To see more info about an item, select it and choose File > Get Info. Get Info has been completely redesigned in iTunes 12 to focus your attention only on what’s necessary for the selected item.

If you’d like to add a field that isn’t visible, click Add Field in the lower-left corner of the Get Info window. You can select additional fields and set fields you’d like to always show. In iTunes 12, Get Info opens on the Details tab, and information about the file can be found on the File tab.

I would also suggest you check the preference settings for iTunes on your Mac. I've highlighted some key information for you below. Click on the link for complete details.

Locate and organize your iTunes files - Apple Support
https://support.apple.com/en-us/HT204668

Copying music to and keeping the iTunes Media folder organized

You can select these options on the Advanced pane of iTunes preferences:

• "Keep iTunes Media folder organized." Learn more about how iTunes 9 and later organizes your media.
• "Copy files to iTunes Media folder when adding to library." Select this option to store all of your media files in the iTunes Media folder. Since they're all in one location, you can easily transfer or back up your media.
  When you import media into iTunes from a CD, it's automatically added to your iTunes Media folder. If you add media to iTunes another way (choosing "Add to library" from the File menu or by dragging an MP3 file into iTunes), it might not be added to your iTunes Media folder.
  

Enjoy!

- Judy