@Tim These are the short terms: “By confirming, you are enrolling in KDP Select. Please note books enrolled in KDP Select must not be available in digital format on any other platform during their enrollment. See the KDP Select Terms and Conditions for more details*.
*If you currently have a book for sale, its KDP Select enrollment is effective immediately. If not, KDP Select enrollment will commence once you publish the book and it is available for sale.”