Sorry for me add description for add book from frontend work good.
That option accessible only at Pro vesrion.
For add self description and other info - you need set "Fetch from" to "from my own"
Other - description - will rewrite with description from Amazon.
Also in Book Library setting - you may found option "Merge description" - if that option turn on - dfescription from amazon will merge with description from user.
How to disable
Article, page break. &Readmore
Please check http://forum.joomla.org/viewtopic.php?p=2449898