Blackjack
Also known as "21" ... the object of the game is to get the closest to 21.
Note that this principal of gambling was known long before playing card were even invented.
An ace counts one or 11 at the option of the holder, and face cards count 10 each.
If you get higher than the dealer without going over, you win - Good luck, and don't gamble. And if you do - remember, the owner of the "establishment" usually gets an appropriate cut.