In the website editor, Pages has a Home page choice once a website has two or more pages. The page you choose moves to the website's own address, and the former home page moves to an address made from its name. This changes the published website at once, and the message after it offers Undo. On a published website, a page has to be published before it can be the home page.
When a page's address changes, visitors who open the old address are now sent to the new one, until another page takes that address. Before, the old address said the page was not found.