The jackpot is triggered by a specific combination of symbols on the reels. When you pull the lever or push the button, the random number generator generates a mixture of symbols. If the given combination matches the jackpot combination, you win big time.
Play Max Lines/Coins: If you're playing a slot with paylines, each one can win independently. That means the more lines you play, the more chances you have of winning. So you're better off playing 20 lines atR$0.05 each than one line atR$1.00. If you're playing with coins, more coins usually unlock the biggest payouts.