The three areas where PHP is used

1. Server-side scripting: PHP is most commonly used as a server-side scripting language. To make PHP work as a server-side scripting language, all you need is a PHP parser, a Web server, and a Web browser. However, the Web server has to have a connected PHP installation.
2. Building client-side GUI applications: Although this is not a preferred use of PHP, with a very good working knowledge of PHP you can build your own client-side GUI applications. You can use PHP-GTK, an extension of PHP, which provides an object-oriented interface for building client-side GUI applications.
3. Command-line scripting: Your PHP script can run without any browser or server. In this way, it can be used as a simple and easy-to-use scripting language for tasks such as managing databases and messaging files.