In slot, the player inserts cash or, in “ticket-in, ticket-out” machines, a paper ticket with a barcode, and then activates a lever or button (either physical or on a touchscreen). The reels spin and stop to rearrange symbols. If a winning combination lines up on a payline, the player earns credits based on the payout table. Symbols vary, but classic icons include fruits, bells and stylized lucky sevens. Many slot games have a theme, and the symbols used are typically aligned with that theme.

The microprocessors in modern slot machines allow manufacturers to weigh symbols differently. So, a single symbol might appear to land on multiple stops on the reels when it actually has a very low probability of doing so. However, the number of possible outcomes is still limited by the fact that there are only 22 symbols.

When a player pushes the play button, the Random Number Generator inside each machine makes a thousand mathematical calculations per second. This information is then used to determine where the reels will stop, and whether the player wins or loses. This is why the house always wins in the long run – casinos don’t make their money by paying out to players, they do it by taking more in than they pay out.