How do I setup the "Look Inside" Feature?

*Update: As of May 17, 20222, KDP has made changes to features available for low content books. These include books with repetitive pages such as notesbooks, journals, planners, etc. The Look-inside feature is no longer available for low content books that do not include an ISBN. If you want your books to have the look inside feature, there is a workaround. You can purchase and use your own ISBN. I recommend using Bowker to do this and to buy them in bulk at a discounted rate.