how does the entire SAT work? i dont know anything about it.?

how does the entire SAT work? i dont know anything about it.?
I dont understand how the SATs work. I really know nothign about them and i need to find out soon since Im going into junior year. For example, I need to know what subjects they test you on, when i should start studying, how do i sign up to get tested, what scores are average, how are they related to the AP courses and their tests and jsut about anything else there is to know about the SATs.

The SAT Reasoning is a long test that tests you using multiple choice questions and a short 25 minute essay. You begin the test with the essay and then get tested on math and critical reading as well as writing. You will be tested on things like Algebra, grammar, vocabulary. To sign up, you have to create a collegeboard account at and then sign up there. The average nationwide score is about 1500 with 500 in each of the three sections (Math, Critical Reading, and Writing). The essay is graded using a rubric. Two graders grade each giving a value from 1 to 6. The two values are added together to give you a score out of 12. A perfect score is 2400. Ask upperclassmen or your counselor for more info. Good luck.