Take a practice test and see how you do. If you score less than a 160, I would recommend taking a Kaplan or Princeton Review study course, but they are expensive. You may be able to get by with books from a bookstore, but if you have a low practice test score, you should lean toward one of the study courses.
Here is the Law School Admissions Council site:
http://www.lsac.org/
There you'll find just about everything you need to know about applying to law school.
You should take the test just in case you do decide to be a lawyer. It's not a test that you can decide to take at the last minute (unless you're exceptionally brilliant). You should spend as much time preparing for it as possible. Keep in mind that in addition to preparing for and taking the test, you'll also have to go through the application process for each school you wish to attend. And, you'll have a write a personal statement.
My friends who are currently law students say to make absolutely sure that you want to be a lawyer before you invest three years of your life in law school. It is a lot of work.
HTH,