Lists are used to organize information in an ordered or unordered fashion. There are three main types of lists in HTML: ordered lists which use numbers, letters, or roman numerals to order items; unordered lists which use bullet points; and definition lists which are used to define terms. Lists are created using tags like <ol> for ordered lists and <ul> for unordered lists. Each list item is wrapped in an <li> tag. Definition lists use <dl> for the list, <dt> for the term, and <dd> for the description. Lists help structure menus, instructions, and other information on web pages.