To win a jackpot you must make a spin with the appropriate qualifying bet for a chance at winning. Each time a player attempts to win, a portion of the bet is added to the jackpot total. As it rises, the one who's spin pushes the jackpot total over its limit will win. You do not have to land on any specific combination in the reels to trigger the feature. This jackpot limit will change every time someone wins to prevent people from knowing when the pot is getting close to paying out. This means the higher the jackpot, the better chances you have of winning.
Jackpots can move from game to game, and are displayed over available machines in the main game lobby so you can see if there is currently a jackpot in your favorite game. Highlighting the jackpot icon will also display the qualifying bet amount.