As far as printing the page that is more of a javascript function.
without seeing your code I cannot recommend proper placement...
but you can simply try to add:
onClick="window.print()
to your submit button.
so:
<form method="post" action="somepage.php">
<input type="submit" name="submit" onClick="window.print()">
// will print the current page you are on (which is what I don't think you want)
so on 'somepage.php' or in your if(isset($_POST['submit'])) { // code...
echo "<script type=\"text\\javascript\">window.print()</script>";