The words all need to be laid out as a book. This means headings, footers, page numbers, title pages (yes, plural) and so much more.
Go get a book in the genre you’re writing in. Look at the first piece of paper after the cover. Probably blank. Look at the next one. Probably NOT blank, and it’s probably not the beginning of Chapter 1, either.
There is quite a bit of front matter to a book. If you’re publishing independently, you need to create this stuff. The publisher’s/legal page. The simple title page and the full title page. Acknowledgments. Table of contents. Index. About the author.
Then there’s page layout. You need headers at the top, with the book title, or chapter title, or author’s name, or whatever will be the most informative for the reader at any given moment.
You’ll need page numbers at the bottom, and perhaps even more to identify the book (stuff that didn’t belong or fit at the top).
Chapter titles, if any, will need to be formatted the same throughout the book. Subheadings, too.
Footnotes, references to other books and resources, quotes, images—all of it needs to be put in place and in shape.
It all needs to be formatted at the size your book will be printed. This is determined by how you’ll print. Online print-on-demand services usually offer industry-standard sizes, but some offer custom sizes as well. If you go for a custom size, have a good reason for it. Being different just to be different is almost always more expensive, or more trouble, or both.
You can’t judge a book by its cover if it doesn’t have one.