So what does PHP exactly do?

[Universe]

That and MySQL...it always confuses me for some reason.

[alvo]

PHP is a scripting language that allows you to write computer programs to do things that are executed by a web server. Writing plain HTML pages gives you a static sote, nothing changes unless you go in and make a change yourself.

Programming languages like PHP, PERL, C and such allow you to manuplate visitor input, stored data, templates and such. For example, this site runs on a PHP script that allows people to post questions and answers, the input is gathered by the script which uses a template to build the pages that you see.

The data for this site is stored in a database (MySQL in this case), the script uses that date to build a page and serve it to a visitor when they ask for it. None of the "pages" on the site actually exist as HTML code anywhere except a visitors browser.