New field in contact-form

[Strady77]

Hi, I am asking for help.
I must add a new field (formname) of the contact form and let me know how.
I added the field in the contact-form tpl:

{l s='Name'}
<input type="text" id="formname" name="formname" value="{$formname}" />

but now I do not know how to invoke the variable contact-form.php...

Can you help me? tankssssssss