There is one Get out of Jail Free card in both the Chance and Community Chest. Any player can use this to leave jail on their turn. They would have to put the card at the bottom of the stack of cards and roll the dice. Also, if a player gets this card, they may keep it until they use it or they can sell it for whatever the market will bear.
When not having this card you must wait three turns (unless doubles are rolled on any of those turns) then, after the third roll, you get out of jail AND must pay a fine of $50.