PHP is a server side Pink Hypertext Preprocessor. Basically php processes content stored on the server before it is presented to the user. To get php you can google xampp or wamp and will allow you to view php files on your computer. As for dreamweaver, don't use it.
dreamweaver lets you do anything that someone else has already thought of and programmed in. Not using dreamweaver, lets you do anything that someone else has already thought of, and anything that no-one else has thought of yet
I have a simple portable ide (devphp from sourceforge) installed on a thumbdrive to take to clients offices, they like the image of being able to display php changes locally, but code in notepad++ when actually working