When you load a page, refresh, anything that requires a page load the page sends out headers to the browser, the headers contain information like header codes - ex. 404 = Not found, 301 = Permanent Redirect, 200 = Success
It also sends out other information, like the information that is being sent when someone presses the submit button on a form. He is suggesting that you get the headers, with the information that is being sent from the affiliates form, once you figure out what is being sent you could, in theory make your own HTML form on your own site, on your own page, completely void of the affiliates page and have it submit/post to the affiliate.
Make sense?