First you should probably try the
NMS version of formmail.pl ... the Readme file of this versions may explain how to use the program a bit better.
I've not used it myself, but by reading the Readme I can see that here are a couple of things to look out for:
When configuring the formmail.pl file, pay particular attention to the @referers variable -- this will be your domain name (without the 'www') or the IP address of the server if you know it.
You might also want to set @recipients to be your own email address to help prevent spam bots from using your form to email other people.
As for the $mailprog variable, you will need to check with your host where your "sendmail" program is installed.
For info on how to format the above variables, see the "COMMON PROBLEMS" section of the readme at the bottom.
I know it's not a step-by-step guide, being that I haven't done it before, but hopefully it points you in the right direction.