Using slots as an example, they generally have three or more “reels,” each of which has a number of symbols. While physical slot machines may have 20 or more symbols per reel, digital technology allows them to have many more—some have 256 virtual symbols—with millions of possible combinations. The combinations of symbols that pay out if you bet on them are called “paylines.”
Slot machines contain random number generators that can generate thousands of numbers per second, each of which is associated with a different combination of symbols. Whether you win or lose is determined by the random number generated in the exact instant you activate each play—if it matches a payline, you win. Since each spin is independent, random and unrelated to previous or future spins, it’s impossible to predict what will happen on each play.
You can see the rules specifc to the game you are playing by clicking the "?"
There are many different kinds of slot machines. Some allow you to choose how many paylines to bet on per play, and how much you want to bet. Before you put your money in, figure out the cost per play, the odds, the paylines, the return to player, and anything else that will help you make the right decisions for you. Look for pay tables in the rules/help of each game.