PHP is a program langague based on c++ that runs serverside which processes text, and outputs it to the user (browser) (used for creating dynamic websites)
HTML is the code which the browser sees and turns into a website. (Also it's what PHP outputs)
XML is pretty much Extensible Markup Language, it's like a big list of stuff to be simply put. It stores data, and provides an easy way for computers to share dataz. (API) and what not.
JavaScript is the client side script engine which helps manipulate HTML, aswell as perform AJAX queries and other cool things.
