PHP is a scripting language. It stands for "pre hypertext processing" which means it is used to generate output before hypertext is processed. Think about it like this: the PHP scripting is used to generate some information. This information can be used to generate output which is added to an HTML document before the HTML document is displayed by your client. All of the work is done at the server, so none of the information is shown to the user.
PHP scripts (programs) are located inside php files, rather than html files. PHP files can contain PHP and html, but html files can not contain PHP. Sounds confusing, but it's not. What this means is that, instead of a file called "index.html", you will have a file called "index.php". Your index.php file can contain all of your existing html, but you can also add in sections that are PHP scripts.
For more information, visit: http://www.hungrybeagle.com/index.php/forum/it11-12-php/6-php-syntax
Things you should know how to do:
- insert a PHP section into a *.php document
- add comments to a PHP section
- enter basic output commands to a PHP section