The player who controlled the ability that restarted the game is the starting player in the new game. The new game starts like a game normally does: Each player shuffles their deck (except the cards left in exile by Karn's ability). Each player's life total becomes 20 (or the starting life total for whatever format you're playing). Players draw a hand of seven cards. Players may take mulligans. Players may take actions based on cards in their opening hands, such as those of Leylines.