Each player loses 1 life. Then, starting with the active player and proceeding in turn order, each player chooses a card to discard (normally without seeing what other players have chosen) and all discards happen simultaneously. Then, starting with the active player and proceeding in turn order, each player chooses a creature to sacrifice (this time players can see what other players have chosen) and all sacrifices happen simultaneously. Then the process that happened for creatures is repeated for lands.