Each individual Jackpot fills up with a percentage of all the bets placed on that specific game mode..
Each roll of the Wheel/Roulette has a fixed chance of triggering the Jackpot. If the Jackpot triggers, it gets split between all eligible users in that round.
Eligible users are players who bet on the corresponding jackpot color for Wheel of Fortune, and all the players in that round for Roulette.
Please click on the Info button next to the jackpot to read the full description.