You've been to Web stores that help you look through large catalogs and purchase items with a "shopping cart." How do they do that? The basic tools are programs to act on your instructions and database management systems to store and retrieve information about the things they offer and the input you provide.
This is a simple example of an interactive page. It uses a programming language named PHP and a database management system named MySQL. These both run on computers where the web pages and the data are stored - they do not require any special help from the visitor's web browser. This is an advantage for websites that are intended to serve the widest possible audience.