[deanhills]

Before installing this plugin I had no plugins installed for the editor and could use it. Why do I need to install another plugin for the editor now?

Does this mean there are no settings in wordpress that can be used without the addition of a classic editor?

You can read the explanation and step by step here.  It came up with my first Google search  

https://kb.yoast.com/kb/how-to-install-t...or-plugin/

Basically the Yoast comes with the new standard WordPress Gutenberg Editor.  And with WordPress if you don't like the Gutenberg Editor you can install the classic editor that will disable the Gutenberg Editor and revert back to the old Classic Editor.