Book Creator makes ‘fixed layout’ e-books. These are books where the author positions text and images on the page, and your readers will see the same layout, exactly what you want for most books containing pictures.
For long books that are predominately text such as novels it would be a big task to layout every page.
If you want to make this kind of ‘flowable text’ book, Book Creator is not the right app for you.
You might prefer to use applications like Apple’s Pages or iBooks Author. Or if you’re using a PC, Microsoft Word or Adobe InDesign.