Nero 7 Ultra MY Audio Book

I have a problem . I don’t understand what Nero wants me to use for sound type in My Audio Book
I burned several mp3 CD’s and made audio CD for users. Then I found “My Audio Book” in Nero and thought it would do a better job. I couldn’t get started because it wouldn’t reconize the sound format or tell me what was required… I know this is stupid to you guys, but it’s bugging me. Heck, I may not even like it. I’d like to decide that for myself. Thanks for listening.
DonKeen