Casinos, cardrooms and poker rooms make money from poker by taking a rake, entry fee or timed fee from the players. In poker cash games, the casino often takes a rake from every poker hand in the room. If a poker room hosts 30 cash games, the casino can profit substantially from this.
They are free, but be sure to tip your waitress, like always. Every poker room I have played there will serve free drinks. Tips will almost ensure timely returns.