According to the php.net Site "PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.
Taken directyle from the php Site "What distinguishes PHP from
on the server, generating HTML which is then sent to the client". The
client would receive the results of running that script, but would
not know what the underlying code was. You can even configure your
web server to process all your HTML files with PHP, and then there's
really no way that users can tell what you have up your sleeve.
PHP can be used on all major operating systems, including Linux, many Unix variants (including HP-UX, Solaris and OpenBSD), Microsoft Windows, Mac OS X, RISC OS, and probably others. PHP has also support for most of the web servers today.
This includes Apache, IIS, and many others. And this includes any web server that can utilize the FastCGI PHP binary, like lighttpd and nginx. PHP works as either a module, or as a CGI processor. So with PHP, you have the freedom of choosing an operating system and a web server. Furthermore, you also have the choice of using procedural programming or object oriented programming (OOP), or a mixture of them both."
What you need to know before starting to learn PHP
Before starting to learn PHP it is important that you have a basic understanding and experience in the following:
Some important facts about PHP