The object of the game is to score the most points by rolling five dice to make certain combination. In each round you start with the same 5 random dice. You must save/select those dice which remain fix and unchanged during next roll. The phone selects its fix dice too :).
The dice can be rolled up to three times in a turn to try to make one of the thirteen possible scoring combinations, since a game of Yahtzee consists of thirteen rounds during which the player chooses which scoring combination is to be used in that round.