The Editor option, also referred to as the Full Site Editor (FSE), is new functionality that is slowly being introduced to enable users to build and extend an entire website using blocks. As the Editor is still currently in its early development stages, you’ll notice a small beta label next to the menu option in the Dashboard. While you’re free to use this functionality on your live website, just be aware that as future versions of WordPress are released, this feature and its functionality, may change.
The new Full Site Editor (FSE) will only be available if you’re using a theme that is specifically built to make use of its functionality, such the default Twenty Twenty-Two theme. For all other (non-FSE) themes, the Editor menu option simply won’t appear. At the moment, there are very few themes available in the WordPress Themes Directory that are specifically built for the new Full Site Editor, but this will obviously improve over time.
Whilst this guide was never intended to be a guide for developers, it will be helpful for anyone who plans to use the Full Site Editor, to have a basic understanding of the different Templates and Template Parts that make up a Theme.