PHP scripts can be coded with in your regular HTML expressions by using PHP tags such as this:
<? CODE HERE ?>
The server will parse the HTML documents for PHP code only if the extension of the file is .php. (.html, .htm, etc will NOT be parsed by default.)
<? date($format,$time) ?>
NOTE: In order to use index.php you need make sure that no index.html, index.htm, index.cgi or index.html file exists
Please click here for the official documentation site on php.net.