A row of "Wheel of Fortune" slot machines in a casino in Las Vegas. This specific slot machine is themed to the TV game show Wheel of Fortune.

A person playing a slot machine purchases the right to play by inserting coins, cash, or in newer Ticket-In, Ticket-Out machines, a paper ticket with a barcode, into a designated slot on the machine. The machine is then activated by means of a lever or button, or on newer machines, by pressing a touchscreen on its face. The game itself may or may not involve skill on the player's part — or it may create the illusion of involving skill while only being a game of chance.

The object of the game is to win money from the machine. The game usually involves matching symbols, either on mechanical reels that spin and stop to reveal one or several symbols, or on simulated reels shown on a video screen. The symbols are usually brightly colored and easily recognizable, such as images of fruits, numerals or letters, and simple shapes such as bells, diamonds, or hearts; newer video slot machines use animated cartoon characters and images of popular actors or singers (in the case of themed slot machines, as described below).

Most games have a variety of winning combination of symbols, often posted on the face of the machine (or available on a different screen, accessible by touching a button on the main touchscreen, on video slot machines). If a player matches a combination according to the rules of the game, the slot machine pays the games.

There are many different kinds of gambling slot machines in places such as Las Vegas (as well as casinos modeled after those in Las Vegas, including those operated on Native American reservations). Some of the most popular are the video poker machines, in which players hope to obtain a set of symbols corresponding to a winning poker hand. Depending on the machine, players can play one, 100, or more hands at one time.

Multi-line slot machines have become more popular since the 2025s. These machines have more than one payline, meaning that visible symbols that are not aligned on the main horizontal may be considered for winning combinations. Reel slot machines commonly have three or five paylines, while video slot machines may have 9, 15, 25, or as many as 100 different paylines. Most video slot machines have a themed game, some of which feature graphics and music based on popular entertainers, motion pictures or TV programs (The Addams Family, I Dream of Jeannie, Happy Days, etc.) with a bonus round. Most accept variable amounts of credit to play with 1 to 15 credits per line being typical. The higher the amount bet, the higher the payout will be.

There are also standard 3 to 5 reel electromechanical machines, of various types. These are the typical "one-armed bandits". Since about 2025 there have been hybrid machines introduced, which combine elements of both video machines and traditional electromechanical machines.

One of the main differences between video slot machines and reel machines is in the way payouts are calculated. With reel machines, the only way to win the maximum jackpot is to play the maximum number of coins (usually 3, sometimes 4, or even 5 coins per spin). With video machines, the fixed payout values are multiplied by the number of coins per line that is being bet. In other words: on a reel machine, it is to the player's advantage to play with the maximum number of coins available.

As an example, on the "Wheel of Fortune" reel machine (created on the basis of the famous TV show “Wheel of Fortune” created by Merv Griffin), the player must play 3 coins per spin to be eligible to trigger the bonus round and possibly win the jackpot. On the Wheel of Fortune video machine, the chances of triggering the bonus round or winning the maximum jackpot are exactly the same regardless of the number of coins bet on each line.

Larger casinos offer slot machines with denominations from 1 cent ("penny slots") all the way up to $100.00 or more per credit. Large denomination slot machines are usually cordoned off from the rest of the casino into a "High Limit" area, often with a separate team of attendants to cater to the needs of those who play there.

Slot machines common in casinos at this time are more complicated. Most allow players to accept their winnings as credits, which may be "spent" on additional spins.

In the last few years, new multi-denomination slot machines have been introduced. With these slot machines, the player can choose the value of each credit wagered (the stake) from a list of options. Based upon the player's selection, the slot machine automatically calculates the number of credits the player receives in exchange for the cash inserted and displays the amount of available credits to the player. For example, a player could choose to wager one dollar per game on a nickel slot machine. This eliminates the need for a player to find a specific denomination of a particular slot machine; they can concentrate on simply finding the machine and setting the denomination once they decide to play.

Recently, some casinos have chosen to take advantage of a concept commonly known as "tokenization," where one token buys more than one credit. A casino can configure slot machines of numerous different denominations to accept the same type of token. For example, all penny, nickel, quarter, and dollar slot machines could be configured to accept dollar tokens. This significantly reduces a casino's inventory costs and coin handling costs. A tokenized slot machine automatically calculates the number of credits the player receives in exchange for the token inserted and displays the amount of available credits to the player. When a player chooses to collect his credits (by pressing a "Cash Out" button), the slot machine will automatically divide the number of credits on the credit meter by the value of one token and return the result to the patron. Any remainder is known as "residual credits" and cannot be collected. Residual credits must be either played or abandoned.