2.Qh5 attacks the pawn on e5 and, with a bishop on c4 to follow, the pawn on f7, which only the king defends. If Black does not see it, Qxf7 is checkmate on move four. That is the whole plan, and against players who have not met it, it works astonishingly often.
Against a player who has, it achieves little. The queen is out early, where Black's pieces can chase her while developing. Black's best answer is simply to defend e5 with 2…Nc6, block the diagonal with …g6 when the bishop arrives, and then develop with gain of time. Knowing that sequence is the point of this page, whichever side you play.