PHP, the term derived from "Hypertext Preprocessor", is a server-side, HTML embedded scripting language used to create dynamic Web pages.
As it's server-side related application it does not require any configuration at the client's/viewer's side since the code itself is executed on the server where it's residing.
All that is required is any Web browser currently existing.
Having the PHP as an embedded implementation at the HTML pages within the special PHP tags at the server side no one would be able to access the code itself through the browser as being able with the plain HTML language.
It's syntax parts is borrowed from other languages as C, Java and Perl with some unique features thrown in.
The main goal of the PHP oriented language is to provide the easiest way of generating and developing dynamic Web pages to the developers or site designers.
The PHP language offers an reliable connectivity services to the various database services like MySql etc. The database management tool phpMyAdmin, most popular bullet in board interfaces like PHPBB or PHPNuke are related on the PHP language as well.
Internet related connection services as e-mail, email via POP3 or IMAP, url encoding, cookies, redirections etc. are available through the PHP as it's web oriented.
Requirements to use PHP
The PHP is the default scripting language implemented with the Apache or any other web server installed at the server where the php should be executed.
If your server supports PHP, then you do not need to do anything. Just create your .php files, put them in your web directory and the server will automatically parse them for you.