To start using PHP and run PHP Web pages you have need three common components need to be installed on your computer system.
Web Server − PHP almost supporting all Web Server software, including Microsoft’s Internet Information Server (IIS) but then most often used is freely available Apache Server. Download Apache for free here − http://httpd.apache.org/download.cgi
Database − PHP almost supporting all database software, including Oracle and Sybase but today most commonly used is freely available MySQL database. Download MySQL for free from here − http://www.mysql.com/downloads/
PHP Parser − In order to process PHP script instructions a parser must be installed to generate HTML output that can be sent to the Web Browser.
Today don’t have need to install php, web server, php parser separately.
For window operating system you can download wampp.
For linux operating system you can download lampp.
For mac operating system you can download mampp.
and Xampp use for cross platform, you can install it into every operating system.