HTML defines six levels of headings. A heading element implies all the font changes, paragraph breaks before and after, and any white space necessary to render the heading. The heading elements are H1, H2, H3, H4, H5, and H6 with H1 being the highest (or most important) level and H6 the least.
Header tags are an important on-page SEO factor because they’re used to communicate to the search engines what your website is about. Search engines recognize the copy in your header tags as more important than the rest. This starts with your H1 and works its way down in importance to the H2, H3 and so on.
While your header tags do extend to H4, H5 and H6, we’re only going to focus on the first three since these are the tags that carry the most SEO value.
How to use H2 and H3 tags
Use H2 for all headings (and H3 for subheadings only).
You must select the title, go to the toolbar -> Paragraph Format and select Heading 2 or Heading 3