Within my themes page.tpl.php file it has a reference to a lot of variables like $head and $local_styles. What file are this variables stored at so that I can looked at what each of these variables represent? John
The values are not stored at all. Instead they are generated dynamically at run time and feed into the template. The list of variables is just there so you will know which variables exactly are available in any particular template.
If you want to examine their content, you can add
to the template, and simply load the page. If you install the Devel module, you can get much easier to read output like this:
I frequently use dpm in my everyday work when debugging or building new code.
The variables are driven by the templating engine. Check out the Drupal API on page.tpl.php for details of what each variable does.