An edition without a manuscript can start one here: "Start writing" makes it with the edition's title page and a first chapter, numbered as books in the edition's language number them, and opens it in the editor.
From there it's a manuscript like any other. Write in the editor; add chapters, parts and pages as the book grows; your changes are kept as you type; "Save as a new version" makes them the manuscript the ebook and print builds, translations and store kits use. You can still upload a manuscript later: it becomes the newest version.
Goals. Set the words you're aiming for in all and each day; the editor shows how far you've come and what you've written today. The focus view hides everything but the page.