Two new items in an editor website's File menu.
Download as files gives the website as visitors see it: one index.html per page, in a folder named for the page's address, with the pictures it uses copied in beside them. While nothing is published, the ZIP is made from the drafts and its name says so.
Switch to your own files turns the website into a files website whose first version is those files. Its address, domain and whether it is published stay the same; from then on you change it by uploading files, and the editor is no longer offered for it. The question before the switch says what changes, because it cannot be undone.