In June 2023 we updated the version of WordPress and included 2 new themes: Twenty Twenty-two and Twenty Twenty-three. These are themes that support Site Editing. This means these themes are a lot more customisable than standard WordPress themes.

As of Summer 2024, the Site Editor is being updated substantially with each new version. We are holding off producing much in the way of help material for now.

Here is a good video on the different between block themes and the older classic themes.

Twenty Twenty-Two is the first-ever default block theme

Twenty Twenty-Three includes a collection of ten community-submitted style variations.

Full site editing’s features, include:

• Site Editor: an editor that allows you to edit all parts of your site, navigate between templates, and more.

• Styles: a feature that allows you to customize your site, including individual blocks, as much as you’d like with different colors, typography, layouts, and more.

• Templates: edit, create, and manage templates used by pages, posts, and other content.

• Template parts: a way to organize and display groups of blocks as part of a block template mainly for site structure, like Headers and Footers.

• Theme blocks including the Navigation block, Query Loop block, and more.

From Twenty Twenty-Three – WordPress.org Documentation

This very short video help understand how Block Themes work January 2024.