There are six types of heading tags in WordPress, and they are H1, H2, H3, H4, H5, and H6. The H1 tag is used for the title and H2-H6 can be used for different levels of headings and subheadings throughout the post.
You don’t need to use all six levels of headings in a post, however, you shouldn’t skip a level. For example, when you use H2 for headings, you should use H3 for subheadings, and not skip straight to H4.