PHP is a widely-used scripting language for web development that is embedded into HTML. It runs on web servers and takes PHP code as input to create web pages as output. To use PHP for websites, you need PHP itself installed on a web server along with having a web browser. This document provides instructions on installing PHP and configuring it to work with an Apache web server on Linux. It describes downloading and extracting the PHP files, editing the configuration file php.ini, and restarting the web server for the changes to take effect.