Gutenberg: The WordPress Block Editor
The way your page looks will vary depending on which theme you're using. For instance, some themes do not have a full browser width option. And there are many other small differences. So remember, how your page looks depends on the theme you're using on your website.
Twenty Nineteen, the default WordPress 5 theme, is a great theme to use if you want to try out the new block editor. Twenty Nineteen theme was designed to work with the new block editor.
You only see formatting options relevant to the element you're editing.
A few page elements have a width option. Many do not.
The old editor looked like a word processor. The new editor does not.
You're unlikely to guess how the new editor works. You'll have to actually learn how it works.
Using just the WordPress Block Editor code named Gutenberg.