Been doing it for about a year. I have had three different opponents so far. It is fun/frustrating too. Basically you go through as much of your hand as possible/reasonable (you'll learn what that is) and then save it back. As the opponent steps through your orders, they choose the actions they want to do. Time Triggers normally get a pause in play.
I'd be glad to play a game with you to get you used to it. It really isn't that different from online play, but just much slower.
Have to run now, but if you want, hit me up on my email: email@example.com
I have played more than 15 games of CC via PBEM vassal over the past 18 months. It is very possible to play via PBEM!!! I have nobody in my area to play face to face, and I find it difficult to find enough time to sit down and play an entire game live via vassal. And, Dan H posted above, you should take him up on his offer, he's a great teacher and knows all the ins and outs of CC.