To publish your book from iBooks Author, you must first export it as a PDF, text file, .ePub, or .ibooks file. To choose what format is best for your book, you should decide how you plan to distribute it.
Publish your book on the iBooks Store
To submit your work for publication on the iBooks Store, save it as an .ibooks or .ePub file.
You can sign up to publish your books directly using iTunes Connect. To sign up to sell your books on the iBooks Store, complete the application and download iTunes Producer. You can also make books available for free on the iBooks Store.
Publish your book on iTunes U
To submit your work for publication on iTunes U, save it as an .ibooks or .ePub file.
To publish your book on iTunes U, you must have an iTunes U site. If you don't have an iTunes U site, you can apply for one.
Distribution on the web
You can distribute works you've created with iBooks Author on the web as a standalone purchase or subscription product or service. When you sell your book on the web, it must be in a non-.ibooks format. Examples of a non-.ibooks format include PDF and ePub. If you wish to sell your work in the .ibooks format, it may be sold only through the iBooks Store. When you provide a work for free, you can distribute it in any format (including .ibooks) through the iBooks Store or by other means.
You retain all your rights in the content of the work you create in iBooks Author. If you distribute your work in .ibooks format, it's subject to the distribution restrictions described above.