The most popular slots are penny and nickel video games along with quarter and dollar reel-spinning games, though there are video games in 2-cent, 10-cent, quarter, and dollar denominations and reel spinners up to $100. Most reel spinners take up to two or three coins at a time while video slots can take 45, 90, and even 500 credits at a time.

Nearly all slot machines are fitted with currency acceptors -- slide a bill into the slot, and the equivalent amount of credits is displayed on a meter. On reel-spinning slots, push a button marked "play one credit" until you've reached the number of coins you wish to play. Then hit the "spin reels" button, or pull the handle on those few slots that still have handles, or hit a button marked "play max credits," which will play the maximum coins allowed on that machine.

On video slots, push one button for the number of paylines you want to activate, and a second button for the number of credits wagered per line. One common configuration has nine paylines on which you can bet 1 to 5 credits. Video slots are also available with 5, 15, 20, 25, even 50 paylines, accepting up to 25 coins per line.

Many reel-spinning machines have a single payout line painted across the center of the glass in front of the reels. Others have three payout lines, even five payout lines, each corresponding to a coin played. The symbols that stop on a payout line determine whether a player wins. A common set of symbols might be cherries, bars, double bars (two bars stacked atop one another), triple bars, and sevens.

A single cherry on the payout line, for example, might pay back two coins; the player might get 10 coins for three of any bars (a mixture of bars, double bars, and triple bars), 30 for three single bars, 60 for three double bars, 120 for three triple bars, and the jackpot for three sevens. However, many of the stops on each reel will be blanks, and a combination that includes blanks pays nothing. Likewise, a seven is not any bar, so a combination such as bar-seven-double bar pays nothing.

Video slots typically have representations of five reels spinning on a video screen. Paylines not only run straight across the reels but also run in V's, upside down V's, and zigs and zags across the screen. Nearly all have at least five paylines, and most have more -- up to 50 lines by the mid-2000s.

In addition, video slots usually feature bonus rounds and "scatter pays." Designated symbols trigger a scatter pay if two, three, or more of them appear on the screen, even if they're not on the same payline.

Similarly, special symbols will trigger a bonus event. The bonus may take the form of a number of free spins, or the player may be presented with a "second screen" bonus. An example of a second screen bonus comes in the long-popular WMS Gaming Slot "Jackpot Party." If three Party noisemakers appear on the video reels, the reels are replaced on the screen with a grid of packages in gift wrapping. The player touches the screen to open a package and collects a bonus payout. He or she may keep touching packages for more bonuses until one package finally reveals a "pooper," which ends the round. The popularity of such bonus rounds is why video slots have become the fastest growing casino game of the last decade.