Header tags are HTML elements used to define headings and subheadings on a webpage. They range from H1 to H6, with H1 being the most important and typically used for the main title. These tags help organize content, making it easier for both users and search engines to understand the structure of the information presented. Using header tags effectively improves readability and accessibility. Search engines like Google use header tags to determine the relevance of content, which can impact a webpage's ranking in search results. Properly structured header tags enhance user experience by allowing readers to quickly scan and find the information they need.