Store settings has a Website row that says where your Store is shown. Show in a website adds the shop to one of your editor websites, or makes a new website named after your Store, with the Shop as its home page and your Store's colours.
While a website shows your Store, your Store's own address and its own domain send visitors to the same page on the website, and new buy links, QR codes, product feeds and search-engine tags name the website. A cart started at the Store's own address still checks out there. The Design band says the website's look is used, and keeps your Store's own design for when the shop is removed.