Php multi variable form problem

Hi there, please, I need some help for my php form. In the zip file I have included a “backend.php” file, that is composed from 3 textfield (I need to add more text field in this form) that will write their content in the txt file named “servizi”, also included in the rar. I’m not so expert with php, so the php form section have some error. This make me really insane, cause I can’t resolve it. Please, could someone help me?
Thanks.