Cards are sold in bundles. You can buy them in many locations in town, at convenience stores, gaz stations, etc. They sell for $10/bundle.
In our case, each bundle has 9 cards in each of 6 colors. So you start with all the blue cards. On the air, they say which type of bingo you play for (straight line, four corners, two lines, around the FREE, full card, etc.) They then call each number and wait somewhere around 15 seconds. And they keep going. When someone has a bingo, they call the station number where someone will check if it is a valid bingo (each card is numbered). They announce on air that there is a potential winner (or winners since it could be more than one) and we get a commercial break for that time. Then, they come back on air to say if there was a winner or not. If not, we continue. If there was, then we change to a different color card, with a different bingo, and so on.
As far as I can understand, this bingo (which is weekly) is used as a fundraiser for the Kinsmen's club and the animal shelter.
You can check their web page.
Other radio stations around here have other bingos.