The SAT is created and administered by the Educational Testing Service, ETS.
The SAT is the "Scholastic Assesment Test." It used to be Scholastic Aptitude Test" but they're dropping the name and just keeping it an acronym. It's the epitome of Standardized tests.
There are 2 forms, the SAT I, which is the one people usually talk about, and the SAT II, which are subject tests. The SAT I is about 3 hours, while each SAT II is one hour.
The test scoring is simple. For every question you get correctly, you get a point added to your score. For every question you answer incorrectly, you lose one quarter of a point. This is to discourage guessing, but you need to get four questions wrong to cancel out the point gained by a right answer. Leaving an answer blank gives you no points, plus or minus. If you can eliminate at least one possible choice with process of elimination, GUESS! Guess by all means, using the remaining answers. Eliminating one answer will boost your odds a great deal, and you'll get a few extra points overall. There, no need to get a review book, now that I've divulged the major secret.
The score you wind up with will become your composite score. It is then taken, and converted to the Scaled Score. The Scaled Score can be between 100 and 800 per section; Verbal, Math, or SAT II section. Basically, your score is on a grade curve. You can't get a zero, so you essentially get 100 points for writing your name,
You'll find registering and sample tests over at collegeboard.com, the official SAT site.
I'd seriously reccomend studying for this test. You have better odds at winning the lottery than getting a perfect score on your first try. Luckily there are many ways about this. Study Books have previous tests and tips. Classes are availible at High Schools and test centers. Websites such as Kaplan.com, collegeboard.com, and princetonreview.com are all helpful.
There are two major players in the SAT study industry: Kaplan and the Princeton Review. Both make it very very simple to master key parts of the test. You can find either in book form, Prep courses, and web site. Both are easy to follow, have a sense of humor, and use similiar methods. Both offer higher scores or your money back. YMMV.
To get a feel for how it influences your college chances, see Median SAT scores for Colleges