Ajax allows web pages to be updated asynchronously by exchanging data with a web server behind the scenes without reloading the entire page. It works by using JavaScript and DOM manipulation on the client-side to update parts of a web page after new information has been received from the server. This tutorial introduces the basics of Ajax and shows how to send and receive data from a server without requiring a form submission. It demonstrates making an XMLHttpRequest object, defining a function to handle the server response, checking the request status, and retrieving the response text to dynamically update an HTML form field.