I think everyone else explained it pretty well. But if you still want a more examples of how it works, here is our linking codes page with several examples of how it can be used:
http://www.threepillows.com/webmasters/linkcode.htm
We recommend affiliates use the &HTML if they want to send the surfer to any page other than the front of our tour (our default). Very handy for a pic of the day BTW, or to send webmasters to our webmaster section, or to send someone directly to the sign-up page - all while planting the cookie so you get credit.
Jimmyf: we had the exact same problem. It turned out there was a flag that needed to be turned on (for each account) for the redirect to work every time. (that was the explanation we were told) I love CCBill but there documentation is not always 100% up to date. We too had to scramble so as to not lose any more $$$ and affiliates from that little mess than we already had before the problem was reported to us.