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.
The most common jackpot amount on a slot machine is typically around 100 times the bet amount. However, jackpot amounts can vary depending on the specific slot machine and the casino. Some machines may have smaller or larger jackpot amounts, but 100 times the bet is a common benchmark.