Each player is initially dealt two cards, one up and one down. There is an initial betting round. Then the dealer goes around the table, asking each player in turn if he'd like another up card. If no one has taken a card, the game is over: Players and the pot is split. If anyone has taken a card, there's another betting round (the as in most games) and the dealer again asks everyone if they would like another card. This repeats until everyone has declined a card; there's no prohibition against declining a card on one round and taking one on another.
You open with a high ante (typically a quarter) to jumpstart the pot, then each player in turn pays a dime for a pair of cards face up. If he thinks that the next card will be between these two cards, he can bet and get a third card. If the third card is between the first two, he wins the amount of his bet from the pot. If the third card is outside the first two, he loses his bet to the pot; if the third card matches one of the first two, he has to pay double his bet to the pot. Since the game is best when relatively large sums are at stake, there are betting limits: 25¢ the first round; 50¢ the second round; $1 the third round; and after that you can "pot it". The game runs until someone wins the pot.
I did a spreadsheet to analyse the odds of winning for each pair of cards that you might see. The results convinced me that you should pass unless the spread between the first pair is 9 (2-Jack, 3-Queen, 4-King, 5-Ace) or better, in which case you should make the maximum bet.