In the top left corner of the room, you can check your statistics that will be displayed in a terminal. You can use Qi coins for gambling, as well as in order to purchase items.
There is an exchange machine to the right from Qi - you can use it to exchange gold to Qi coins, the exchange rate is 10:1. To access it, you have to complete “The Mysterious Qi” quest: otherwise, the Bouncer won’t let you in. You can access the Casino through the back door of Oasis, in the Calico Desert.