To bet is to gamble or risk something valuable against an unknown outcome. Poker players bet on each hand, hoping the cards they hold will beat those of the other players. Sometimes you bet money on a sporting event, wagering on the team you think will win and collecting even more money if it does.
One player sits behind the game unit with their head under a water container. Yup &you guessed it! If the person in the hot seat can't meet the number of items their teammate predicted they'd guess, they'll eventually get the drop! The container tips and dumps water on that player's head.