The Law School Admission Test (LSAT) is required for all law school applicants. The LSAT is administered through the Law School Admissions Council (LSAC). LSAC provides sample LSAT questions, study guides, law school research tools, law school forum calendars, and the application Credential Assembly Service (CAS). Registering with LSAC is required to take the LSAT and to apply to submit application. Simply log on to LSAC.org to start the process.
There are two approaches to timing. One is to take the test the June after your junior year. This gets the test out of the way in the summer; the June test is usually administered in the afternoon; and if something goes wrong, you have time to recalibrate and retake the test in September or November. In the alternative, you may aim to take the test in September or November to maximize study time. In either event, you should only take the test if you are sure you are ready. LSAT scores stay on your record for at least five years. While most schools look at the highest LSAT score, they will see them all, and you don't want them to be guessing which one represents your true ability.
While there is little empirical evidence about how many hours a student should devote to studying for the LSAT, this office recommends that students develop a study plan in the fall of their junior year and start to familiarize themselves with the material no later than December of their junior year (the brisket method: low and slow).
Some students choose to study for the exam on their own. You can purchase study aids (books) and actual old exams through retailers such as Amazon.
Many students, however, opt to take a commerical test prep course. These courses are offered in a variety of formats (in person, synchronous online, and asynchronous online) from a variety of vendors at a variety of price points. This office recommends that you research these companies carefully before making a decision about taking a course. Do this research no later than Fall of your junior year so that you have time to identify a course that is convenient and that you can afford. Be aware that these courses are often quite expensive (often over $1000). You might want to start saving for LSAT preparation and law school applications early in your college career.
However you choose to prepare, the key is to prepare. While it is not the only component in your application, this single test has an undue effect on your future, and a low test score may prevent you from getting into the school of your dreams. You should give it the attention it deserves (and requires).