One of my favority aspects of PHP is the phpinfo function. It gives you all sorts of information about your server environment, curent request, etc. Whenever I move to a new server or help someone troubleshoot PHP, the first thing I do is create the following simple PHP file to see everything there is to see about their install:

<?php
    phpinfo();
?>

If you’re only interested in a subset of this information, you can sepecify this with a flag. For example, during development it’s useful to see what server variables are available with the current call. I often include the follwing at the bottom of my document (using the INFO_VARIABLES flag):

...
<?php
    phpinfo(INFO_VARIABLES);
?>
</body>
</html>