HTML is a markup language used to create web pages. It uses tags like <html>, <title>, and <body> that are placed within angled brackets to denote elements on a page. Tags can be container tags, which have an opening and closing tag to surround content, or empty tags which are standalone with no closing tag. When creating an HTML file, it should be saved with a .html or .htm extension and then can be viewed by opening it in a web browser.