•We might find a suitable answer for this question from the answer to the question “What can PHP do?”.
•According to PHP official site, PHP can do anything. PHP is mainly focused on server-side scripting, so you can do anything any other CGI program can do, such as collect form data, generate dynamic page content, send/receive cookies. But PHP can do more.
•There are three main areas where php script are used.
•Server-Side Scripting: This is the most traditional and main target field forphp.
•Command Line Scripting: You can make a php script to run it without any server or browser. You only need the php parser to use it this way. These scripts can be used for simple text processing.
•Writing Desktop Applications: Actually, PHP is not the very best language to create a desktop application with a graphical user interface. But if you know php very well and would like to use some advance php features in your client-side applications, you can use PHP-GTK to write such programs.
•PHP can be used on all major operating systems including Linux, Unix, Microsoft Windows, Mac OS X, RISC OS.
•PHP is an OPEN SOURCE language. Which means that you are free to use, develop, and distribute without having any license issues, of course you should read any software privacy and license before use or distribute it.
•PHP equipments: server, parser, are free to use and distribute, by a license from PHP official site.
• To download and install server on your localhost, I recommend using AppServNetwork at http://www.appservnetwork.com/ go to downloads page and download server suitable to your operating system.
PS, download this lesson as PDF file PHP Tutorial – Lesson 1: Introduction to PHP – Part I