HTML is the language used to structure and present content on the World Wide Web. It uses tags to define headings, paragraphs, lists, and other elements. A basic HTML file includes an <html> tag which contains <head> and <body> sections. The <head> includes the <title> and the <body> holds the visible page content. Common tags include <p> for paragraphs, <ul> and <ol> for unordered and ordered lists, and <img> to embed images.