The plugin hooks in the WordPress wp_star_rating() function and adds a custom field where a number between 1-5 is input. That number is then translated into stars and becomes the rating for the book or other item. In my unreleased project, this is added automatically to the record. In this standalone plugin, buttons are added to the toolbar that can be used to add the shortcode that will display the code.
There is more information in my article here.