Exact location of CI files

That is the idea. If you are using .htaccess to hide "index.php" in URLs, it would go inside public.
You would map your domain DocumentRoot to "mysitename.com/public/", not "mysitename.com/", and you should be in business.

ps The CodeIgniter 4 reference is *only* for the folder structure. It is a rewrite, and there will be many more changes, compared to CodeIgniter 3