When you code in php, the php does not display the error message when there are bugs in the php code. Instead of debug message, you receive a message telling you that Internal Server error (HTTP 500): An unexpected condition was encountered while the server was attempting to fulfill the request. By default the debug message was turned off because you do not want users (hackers) to see the debug error messages.
If you want to turn the feature on, modify the php.in file and set the php_flag display_errors to on.
php_flag display_errors on