If I had to guess, there’s probably a dozen things missing. Plugins not baked into your app, initializations of some settings, adding other php units in the uses - do the tutorial and follow along the same steps in your app. Or even once the tutorial is done just change it to what you want - it may be easier to knock out stuff in a working app than to try to work it out from scratch.
static files like CSS, JS and images should be handled by the webserver itself, not CakePHP.
So make sure your webserver configuration (vhost config) is set correctly so your docroot folder path is set to either the “root” directory or the webroot directory.
Basically you should be able to call e.g. http://localhost/css/cake.css and the browser should show you the CSS file.