Users of the device would deposit their wager, in an amount of money requested by the device, into it and then pull a lever located on the side. The machine would then display random and independent images on its front, and if those images formed various combinations, the user would be considered a winner and receive an amount of money proportional to the odds of the image sequence appearing. As with most forms of gambling, the odds were not in the user's favor.
Vic's lounge, within the Vic Fontaine holoprogram, also had slot machines. Kasidy Yates used one of them while trying to distract to the security guard guarding the count room during a scheme to rob the casino. (DS9: "It's Only a Paper Moon", "Badda-Bing, Badda-Bang")