Understanding How PHP and MySQL Work Together
WordPress uses a PHP/MySQL platform, which provides everything you need to create your own blog and publish your own content dynamically, without knowing how to program those pages. In short, all your content is stored in a MySQL database in your hosting account.
PHP 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 like Greek to you, just think of MySQL as a big file 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 a host server. The PHP programming language receives that request, makes a call to the MySQL database, obtains the requested information from the database, and then presents the requested information to your visitor through his Web browser.
Here content refers to the data stored in the MySQL database; that is, your blog posts, pages, comments, links, and options that you set up in the WordPress Dashboard. However, the theme (or design) you choose to use for your blog — whether it's the default theme, one you create, or one you have custom designed — isn't part of the content in this case. Theme files are part of the file system and aren't stored in the database. Therefore, it's a good idea to create and keep a backup of any theme files that you're currently using. See Book VI for further information on WordPress theme management.
When you look for a hosting service, keep an eye out for the hosts that provide daily backups of your site so that your content (data) won't be lost in case something happens. Web hosting providers who offer daily backups as part of their services can save the day by restoring your site to its original form. Additionally, Book II, Chapter 5 covers important information about backing up your Web site.