While H1 corresponds to your title, H2 and H3 correspond to your headings and subheadings, respectively.
The H1 should be descriptive of the page’s content and you shouldn’t have more than one H1 per page. Choose your title carefully and don’t forget to include your main keywords. Following your H1 in the hierarchy of headers is H2, H3, etc. While H1 corresponds to your title, H2 and H3 correspond to your headings and subheadings, respectively.