Black's queen and knight are both under attack. If he tries to save his knight and counter-attack White's queen by 17...Nb5, then Byrne planned 18.Bxf7+!, and if 18...Kxf7 then 19.Qb3+, saving the queen with check, followed by taking Black's queen. Byrne probably thought he had outwitted his thirteen-year old opponent. But it turned out that Fischer had seen everything!
White has taken the queen. But now Fischer starts a windmill attack...White is in for a bumpy ride!
White has a queen, and Black does not. But If you count up the material, you will see that Black has a rook, two bishops, and two pawns for the queen. The queen is a powerful piece, but it cannot compete with such an army! So in fact the position is completely hopeless for White. But he did not give up. Maybe he was hoping a young boy might lose concentration and make a blunder. But instead Fischer finished the game in style.
When this game was played, Fischer was rated only 1726. That may seem like a lot, but actually it is far below the level of even an average master. But at that time ratings were published only once a year, so clearly Fischer was playing better than that! About a year later he became the U.S. Champion, and sixteen years later - champion of the world.