This section only appears if you are entering the details for an e-book.
You can choose to make your book available immediately or set a future release date with pre-order availability.

If you choose to enable them, customers will be able to pre-order your e-book for up to a year in advance of the publication date. An Amazon sales page will be created in order for customers to pre-order the book. The book will not be available for download until the publication date. On that day, Amazon will automatically send your e-book to all customers who pre-ordered it.

Amazon enforces strict rules around pre-orders. For example, if you choose to cancel a pre-order, perhaps by deciding not to publish your book, you will be prohibited from setting up new pre-orders for one year.
Find out more about pre-orders here: https://kdp.amazon.com/en_US/help/topic/G201499380
At the bottom of the page, click ‘Save and Continue’ to move on to the Content section of the process.
Continue to the next lesson to learn about Publication Dates and Release Dates for hardback and paperback books. Alternatively, head to the next section to begin entering the Content of your book. For e-books, this will start with the Manuscript section.