To add and edit new books go to Entries > Books. Once there you can edit an existing entry by clicking it's title or creating a new entry by clicking the New Entry button at the top right.
Content fields are organized into 3 different tabs. One for Content, Sidebar, and SEO. Content is the main content of the page, sidebar contains content on the sidebar, and SEO is custom SEO input.
Enter the content in the various fields. Be sure to set your focus point for the book cover if you are using that for the SEO image as well.
If you have a custom SEO image, switch to the SEO tab and upload it there.
The hero image for the book detail page can be changed by going to Globals > Book Detail Hero and changing the image. This image is used on every book detail page.