They must bid how many dice they think have been rolled among all of the available dice. Whoever lost a die most recently (first round, just pick someone randomly) starts the round. Each round starts with all of the players rolling their dice.
In Perudo, each player starts with five dice and a cup (to keep their dice secret).
One of my favorite party games that I'm glad to get to tell you about is Perudo (also know as 'Liar's Dice').
