In a physical casino, you spin the reels by either pushing a button or yanking on a lever, whichever you prefer. In an online casino, you would use your mouse to click on the button or lever. There is a horizontal line across the window of the slot machine. If a certain combination falls on the horizontal line when the reels stop, you are a winner. Payouts vary by machine.
Slots generally fall into two categories - straight slots and progressive slots.
A straight slot will pay your winning combinations according to a predetermined schedule. A progressive slot machine will pay you in a similar way unless you hit the progressive jackpot. When you hit the jackpot, you typically win a huge sum of money. In a progressive slot game, a percentage of each coin dropped in the slot machine is added to the jackpot. If no one hits a jackpot in a while, it can grow to be quite large.