If you are going to take it this school year, you'll want to get registered pretty soon. It's offered on May 3 and June 7, and then not again until October. Registration deadlines are about a month before the test is administered. Here's a link to the calendar and registration info.
SAT Dates - SAT Test Dates and Registration Deadlines
It is awesome that you're thinking toward college in your sophomore year; you're already a bit ahead in the game, and you have time to explore your interests and build up a great resume. And if you can get most of the testing out of the way by the end of your junior year, you'll have a calmer and happier senior year. Good luck on your tests and in your future studies!
