The topic is used in the email subject line so you can tell which form the message comes from. This is very useful if you have several such forms. The message field gets put into the body of the email. I am assuming you have read the online docs on FORMs . The Topic is used on the email subject line so you know which form sent the mail.
Message is optional.
It will send email to you with the results. Any extra fields will be added to the top of the message in alphabetical order. Here's a sample HTML file that uses Feedback Form . Note that the email address in the FORM tag is bogus, so you will need to supply your own. Click here to see the form.