PHP is an open-source general-purpose scripting language that is suited and popular for server-side Web Development. There is an excellent online manual and a wiki. The online manual is a complete reference for syntax, built in functions, and extensions. There are lots of extensions for PHP that most of them can be find in PECL.
If you want to post a question in PHP, check the error log or if errors are enabled, enter them from output of your script if any.