OOP design question

I am starting to get a handle (I think) on OOP. I was wondering if anyone would care to comment on what I think I understand: For simplicity's sake class.php contains AddItem() and DisplayItems(). Since submitting form data <?php include('class.php'); If(!$_POST['submit']){ //Do I need to instantiate(?) $po everytime the page reloads? $po = new PO; } If($_POST['submit']){ $po->AddItem(); } <form action="$PHP_SELF" method="POST" > ...form fields and a submit button... </form> $po->DisplayItems(); ?> Is this a good basic methodology (aside from checking the form fields for valid characters). Thanks, Mike Smith