Paragraphs are defined with <p></p> tags. The paragraph tag tells browsers to add an empty space in between paragraphs. Though most browsers will format paragraphs correctly without the closing tag, not all will, and the formatting of the entire page can be affected. Do not forget the closing tag.
<p> This is one paragraph. </p>
<p> This is another paragraph. </p>
<p> This is a third paragraph. </p>