Once your payment is made, the download link will be immediately provided to you on the Checkout Success page. If paying by Check or Money Order, the link will present itself on your "My Account" page after payment has been received.
You can log into your account using your email address and password you used when you placed the order and once logged in, go to "My Account" and click the button that says "View", located under "Previous Orders". You will see a button that say "Download". Click it to download your book.