Important PSAT/SAT questions please help?

I am an upcoming sopre (10th grade) in high school, and I want to know more about the PSAT taken in October of sopre year. Is it important? Does the score that you receive count for anything? Is it true that if you get a high score on it you may be eligible for a scholarship? Also, I heard there is also a PSAT test during junior year (11th grade). What is the importance of that one? Is the actual SAT taken during senior year (12th grade)? And what are ACTs? Please help!