I want to ask that what's that multiple bids that get added to the jackpot?
All the bids form all participants increase the jackpot. Multiple bids means that if your bid is no more the highest bid at some point in time, you can bid again if you want.
How can people compete when they will be able to see the current highest bid?
The highest bid is displayed to let participant know which amount they need to outbid in order to win.