Headings and Hierarchy
So you want to call attention to something. You use a heading so that it shows bigger, right?
Wrong!
Notice that the word "wrong" above is not a heading, it is paragraph text that has been bolded, and it's font size was changed in the block settings. Use this technique instead of creating a heading if you absolutely must 😉
Proper use of headings
Headings need to be used to convey information hierarchy so that screen readers, "Reader View", and search engine crawlers can understand how the page is structured. An h1 tag is reserved for the title of the page, and should never be chosen from the list in the block editor. An h2 tag denotes the title major section, with an h3 being the title of a section within that, and so on. Here is an example of proper use of headings and sections:
Top level section heading (h2)
H2 headings are the most commonly used, and denote the title of each section within your web page. The block editor defaults to h2, which is very helpful.
Subsection Heading (h3)
The h3 heading should be used when your top level section has sections underneath it. An analogy would be a bulleted list in Word, where you have bullets or numbers underneath the main bullet.
Sub-Subsection heading (h4)
If you get to the point where your sub-sections have sections, use h4 in the same way to denote content sections underneath your h3. H4, h5, and h6 are also available, but the use cases for those would be extremely limited.
Information Hierarchy
When writing a term paper, there is generally an introduction then sections based on the main ideas in the intro. A web page should be structured like this as well. As mentioned before, users viewing the page with screen readers will have a much better experience. Switching to "Reader View" in your browser will hide all special formatting and reveal the actual structure of the page, which is ideal for printing. Search engines will be able to find and recognize content better, so that when users are searching for something specific it will show closer to the top of search results.