An HTML tag has attributes that describe its characteristics and a syntax that defines its structure. Common paragraph tags include <p> and </p> to create paragraphs and <dd> to indent the first line. The <blockquote> tag indents both margins. The <br> tag creates line breaks without a closing tag. Formatting tags like <b>, <u>, and <i> make text bold, underlined, or italic. The <font> tag applies specific fonts, colors, and sizes by using attributes like color, size, and face within the start and end tags.