WordPress Full Site Editing (FSE) is essentially a continuation of the Gutenberg project. It’s a feature that uses the block content editor interface for WordPress.org’s built-in website and theme customization tools.
This means you can use the block content editor not just for creating your page or post content but also for a header, footer, sidebar, and more.
The goal of Full Site Editing is to simplify website building in WordPress. While WordPress is pretty user-friendly, it wasn't always the easiest to use for beginners.
For starters, the previous Classic Editor is quite barebones. When you create a new page, you can't see what it looks like right away. Instead, you have to switch back and forth between the preview page and the editing interface to see the page’s appearance on the front end.
Some people also find the WordPress Theme Customizer limiting as it doesn’t have a drag-and-drop functionality.
In other words, you can’t move and edit elements around exactly how you want to. That’s why many people install a WordPress page builder plugin to get more flexibility in their design.
The Gutenberg project aims to solve these problems by introducing newer, more user-friendly website-building tools, including Full Site Editing.
With FSE, beginners can create their WordPress websites using an easy drag-and-drop block editor and see a live preview as they make changes.