Tutorial on Re-filling form data?

Using PHP 5 and not OOP savvy.

I have a form that gives the user options. On submit it calls itself
and if the $_POST variable is set produces the result of the form
choices. However, it currently resets all the form options to default
values.

Is there a tutorial somewhere on how to keep the existing form choices
in place, unless the user changes the selection and resubmits?

Thanks!

Leam