The WordPress software is a personal publishing system that uses a PHP-and-MySQL platform, which provides you everything you need to create your blog and publish your content dynamically without having to program the pages yourself. In short, with this platform, all your content is stored in a MySQL database in your hosting account.
PHP (which stands for PHP Hypertext Preprocessor) is a server-side scripting language for creating dynamic Web pages. When a visitor opens a page built in PHP, the server processes the PHP commands and then sends the results to the visitor's browser. MySQL is an open source relational database management system (RDBMS) that uses Structured Query Language (SQL), the most popular language for adding, accessing, and processing data in a database. If that all sounds Greek to you, think of MySQL as a big filing cabinet where all the content on your blog is stored.
Every time a visitor goes to your blog to read your content, he makes a request that's sent to your server. The PHP programming language receives that request, obtains the requested information from the MySQL database, and then presents the requested information to your visitor through his Web browser.