Document Body tags
HTML provides six levels of heading tags (<H1>-<H6>). All levels are rendered larger than surrounding text, with the lowest level rendered at the largest size. Heading tags also insert vertical space between the text marked and the surrounding text.
You should avoid skipping levels to achieve a certain visual effect as there is no guarantee how the headings will be rendered on any given system. They are intended to indicate document structure.
Here is a markup example along with tagged examples for all six levels: