I might be being stupid here but I though Caravan was poker similar to Texas Holdem.
Caravan is like poker combined with blackjack, combined with a trading card game.
You have decks that you build yourself- you actually find the individual cards in the world and can put them into your deck. Then you can challenge people to play caravan- they have their own decks. I assume difficulty is adjusted by more difficult players having better decks.
Then you draw your decks, playing a sort of blackjack with yourself, and your goal is to get 26 with three different piles of cards. Each pile is called a caravan. You can't stay until you have over 21 either. They play at the same time and whoever gets closest to 26 without going over wins.
You can strategically build your deck to get different types of cards. I think you can't have dupes of the same card though.
That's the basic gist of it. There are some more complicated rules, like what you can put down each turn, but basically when you draw, you start your caravans, and subsequent cards have to be higher or lower, giving the caravan's direction, and matching the cards' suit.
Face cards do some specific things to the caravans, but I don't remember them.