HTML is the standard markup language used to create web pages. It uses tags to describe and define the structure of a web page. Some key HTML tags include <html> to define an HTML document, <head> for metadata, <title>, <body> to contain the visible page content, <p> for paragraphs, <h1>-<h6> for headings, <a> for links, and <img> for images. HTML is written by enclosing tags in angle brackets within a text editor and saved with an .html file extension. Common HTML tags were demonstrated like headings, paragraphs, links, images, and basic formatting.