This HTML form tries to submit the data to
which does not exist, so you get a error message if you click submit.
So before using it, you have to replace the URL http://www.example.com/cgi-bin/whnmail.pl
in the HTML code of this page by the URL where you actually upload the script.
In order to use it, you have to copy the source of the perl script from whnform.txt to http://www.example.com/cgi-bin/whnmail.pl (or whatever else your server address might be) and set the script to executable.
Once you have done this, you can use the script so mail form data. You should also add your own e-mail address in the source of the script, since otherwise the e-mail are sent to firstname.lastname@example.org instead of your address.
After you install the script and make it executable, its source code can be viewed by everyone at an URL of the form http://www.example.com/cgi-bin/whnmail.pl?source where of course www.example.com has to be replaced by your domain.