Basically, Double Joker Poker plays out like any video poker game. Choose your wager (max coins gets max payout on the royal flush, remember) and you are dealt five cards. You may also discard and draw between zero and five cards; you receive the appropriate number of cards to fill out your five-card poker hand.
The two jokers added to the deck are wild cards and may represent any card you wish; typically the cards "speak for themselves" as they say and so the game will decide your highest possible hand.
In double joker poker, the paytable is a bit different, too. Pairs of any sort are no longer paying hands and five-of-a-kind is now on the table as well.