It's a classic game of Blackjack just you against the dealer, the rules are:
Dealer must draw to 16 and stand on all 17's.
Whoever is closer to blackjack (21) without going over 21 wins, blackjack pays 3 to 2 and other wins are 2 to 1 so you at least double your money for each win.
No real bitcoins. All virtual.