Headings help to introduce new sections and organize the content on the page. They make your website more readable by humans and search engines.
To add a heading, click on the Block Inserter (+). Alternatively, you can type /heading in a new paragraph block and press enter.
You can also add a Heading block with H1 heading level by typing /h1 in a new paragraph block followed by enter. Subsequent heading blocks can be added by typing /h2, /h3, /h4, /h5, /h6 followed by enter.
The Block editor by default considers the page title as the <h1> tag, so subsequent Heading blocks are added as H2, H3, and so on.
You can also choose your heading level according to your style from the Block Toolbar.