AP,
First, you'll need an opponent with the Gold Demo. Start a thread over in the "Opponent Finder" section and I am sure somebody will turn up.
At that point, one of you starts a scenario (choosing multi-player/email) and then proceed normally from there. BTW, you'll be exchanging three files per turn.
I hope that helps.
If you need more specific help, feel free to email me (superted@combatmission.com).
Good luck!