Here is a simple set of examples. The first form collects the submitter's name, the second collects their email address, and the third their sex, which then sends it on for final processing (i.e. sending emails, logging, etc). Obviously real world situations are going to be a lot more complex than this.

form_part1.html

<form action="/cgi-bin/formprocessorpro.pl" method="POST">
<input type="hidden" name="_browser_out" value="form_part2.html">
Your or Company name: <input type="text" name="r_yourname">
</form>

form_part2.html

<form action="/cgi-bin/formprocessorpro.pl" method="POST">
<input type="hidden" name="_browser_out" value="form_part3.html">
<input type="hidden" name="r_yourname" value="[r_yourname]">
Your e-mail: <input type="text" name="re_email">
</form>

form_part3.html

<form action="/cgi-bin/formprocessorpro.pl" method="POST">
<input type="hidden" name="_send_email" value="email.txt">
<input type="hidden" name="r_yourname" value="[r_yourname]">
<input type="hidden" name="re_email" value="[re_email]">
Sex: <select name="r_sex">
<option value="Male">Male</option>
<option value="Female">Female</option>
</select>
</form>

This works because when the _browser_out text file is parsed, Form Mail: eMail Form Processor Pro will fill in the values in the square brackets from what the user entered.