no, psat is not required for every high school student. But it is a great way to practice and learn what's on the sat when you take it later. The questions on psat are similar to those on the sat, and usually people get a low score on psat and then they go over which they got wrong and practice on that, and when they take the sat, they will get a better score.
plus, when you take psat in eleventh grade, if your score is high enough, you will be seleceted as one of nation's merit scholar, it's a great honor and colleges will give you a better chance than someone who is not a nationalmerit scholar.