What is PHP ?
PHP is a powerful server-side scripting language for creating dynamic and interactive websites. PHP was created in 1994 by Rasmus Lerdorf to track the visitors to his online resume; thus, it originally stood for Personal Home Page. As its capabilities grew (and as more people started to use it), it came to stand for PHP: Hypertext Preprocessor, which basically means that PHP handles data before it becomes HTML (HyperText Markup Language).Since it's a preprocessor, it runs on the remote web server and processes the webpages before they are sent to the browser. This makes it a so-called server-side scripting language.
PHP is the widely-used, free, and efficient alternative to competitors such as Microsoft's ASP. PHP is perfectly suited for Web development and can be embedded directly into the HTML code. Here are some resources and downloads for PHP
Download PHP Here
FAQ on installation and Download
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, or send and receive cookies. But PHP can do much more.
PHP is capable of generating dynamic HTML pages and hence it can output HTML which servers as a presentation layer and in the backend, on the server it can continue to process all requests made by the client. These requests could be processing of form, handling cookies, uploading files, generating dynamic HTML by querying a database etc.
PHP can also be used from command line to execute php scripts. This is similar to running a UNIX shell or a perl script from command to accomplish tasks like taking backup of files, analyzing log files, generating a list of files and folders etc.
PHP is capable of doing much more than what read above. You can use it on command line interface to do most of the tasks stated above, without a browser, of course. PHP can also be used to create rich GUI applications using PHP-GTK kit. This requires knowledge of advanced PHP features.