1) I added "<?php @sessi?>on_start();" after line 5 as your instruction.
2) As you are writing "Then on your page somewhere you can see it add this",
I am not sure what it stands for or indicate and where I should insert the php statement into a registration.php:
echo("failed: " .ValidatedField('registration','registration'));
Anyway, I put 2 php statements into the registration.php and attached the ragistration.php
Thank you for looking into my problem.