PHP Form Mailer

I’m trying to use your PHP Form Mailer and I was wondering on how to add more fields to the PHP page. I know how to add them to the actual form but not sure how to do that into the code of the PHP page. Or If I need to add any other code to the PHP page at all even if I add input fields to the form.

This is the link where I found
your form: http://www.kirupa.com/web/form_mailer.htm

Thanks