The PSAT and PLAN are exams that provide a preview of the SAT and ACT, respectively. They are a good way of taking a practice exam under normal test taking conditions. The score you get has no impact on college admissions directly. You will get the score back a few months later with a breakdown of how you did. The PSAT does not have the essay portion from the SAT, so it isn’t completely indicative of the score you will actually get. I highly recommend taking the test for the first time in 9th grade and then taking it again in 10th and 11th.
The PSAT also functions as the National Merit Scholarship Qualifying Test. It only serves this dual purpose in 11th grade, and requires no additional paperwork. Your score is compared with others from your state, and if it is above the benchmark they have decided for your state, you are awarded the designation Commended Student. If your score is above a second benchmark, you are a semifinalist in the scholarship competition. There are then additional requirement for students to fulfill to become a finalist.