The Visual Editor is the WYSIWYG (what-you-see-is-what-you-get) mode in WordPress, showing your content formatted the way it will actually appear on the live page, rather than raw code.
This is the default experience most people use when writing posts — bold text looks bold, headings look like headings, all without needing to understand any underlying HTML.
Visual Mode vs Code Editor
The block editor also includes a Code Editor mode, which shows the raw HTML and block markup behind your content. Most everyday writing happens in Visual mode, while the Code Editor is more useful for developers or advanced troubleshooting.
Switching Between the Two
You can toggle between Visual and Code editing from the options menu in the top-right corner of the editor. Switching back to Visual mode after making manual code edits lets you confirm everything still displays correctly.