Firstly, while ASP is different from HTML, it is usually written as scripts within an HTML document. HTML is a static document that the Web server displays upon request by the browser. But if the HTML has ASP scripts embeded within it, the server will run those scripts and then display the results within the page on the browser.
ASP is a powerful tool for Web developers. If you have access to an IIS server or Chili!Soft ASP server you can make your sites dynamic, personalized, and interactive quickly and easily.