Click on the icon to create a new form. In Design view, the form is outlined by a dashed red line. Once you've created a form, right click on the dashed red line outlining the form and select "Action...". This pops up a menu like this:
In the "URL" textbox, type in "/cgi-bin/BFormMail.pl".
In the "Relative To" dropdown menu, pick "Site Root".
Alternatively, you could type "/cgi-bin/BFormMail.pl" in the "Action" textbox of the Properties form.
Below is a list of functions that BFormMail can perform, along with examples and code for each function.