Headings can help structure your page and make your content more readable by humans as well as search engines.
Get started by clicking the + Inserter icon 
at the bottom-left corner of the screen and select the Heading Block from the blocks list
Once you add a Heading Block and add the heading text you can then access the text settings at the bottom of the screen.
You can also change the heading size. Headings are added as an H2 by default, which make them just a little smaller than the post or page title, but you can change the size by selecting other options available
