The Armed Services Vocational Aptitude Battery (ASVAB) is a multiple choice test, administered by the United States Military Entrance Processing Command, used to determine qualification for enlistment in the United States Armed Forces. It is often offered to American high school students when they are in the 10th, 11th and 12th grade, though anyone eligible for enlistment may take it.[2]

Unlike enlisted applicants, officer candidates are judged solely on their General-Technical line score and not their AFQT score. Remember, the General-Technical score is comprised of the sum of Paragraph Comprehension, Word Knowledge, and the Arithmetic Reasoning subtests. The GT score requirement for prospective officers for each branch is detailed below. Note, the Air Force and the Navy do not use the ASVAB for officer applicants and rely on their own exams. 

You’ll need to bring valid identification (photo ID, SSN card) to be admitted into the ASVAB testing room. Arrive on time— you’ll be turned away and required to reschedule if you are late. Your recruiter may give you a ride to and from the session, but he/she is not permitted in the testing room. You will not need to bring a calculator for the test.
AFQT scores are reported as percentiles between 1 and 99, and the score is relative: Your AFQT score indicates how well you did compared to the scores of a reference group. For example, if you score 71, that means you scored as well as or better than 71 percent of those in the reference group. If you score 50, your score is exactly average compared to the reference group. According to the Army, about half the population scores at or above 50, and about 16 percent of the population scores at or above 60.
Retesting is possible depending on a variety of circumstances. It is possible to retake the ASVAB or PiCAT, but you will need to coordinate this with your recruiting office. In general you may be required to wait a month or more to retake the test; each branch of the service may have different requirements that must be fulfilled in order to retest.
Don’t let the PC section of the test throw you for a loop. Unlike the individual multiple choice questions in other sections, here you will need to read a paragraph and answer several questions in a row based on that one paragraph. The people who designed this section of the exam really knew how to make sure you are able to read detailed (and often boring) documents, remember the details of what you read, understand why they’re important, and be able to pick out the key concepts they illustrate. When you read each paragraph, it’s helpful to know the kinds of questions you’ll be asked at the end. There are basically four kinds of questions to test your comprehension:
If you are interested in joining the military then the Armed Services Vocational Aptitude Battery (ASVAB) may, very well be, the most important test you'll ever have to take. Spanning everything from job selection and pay grade to serving in the branch of your choice or even serving at all, the importance of the ASVAB cannot be overstated. The primary function of the ASVAB is to determine if recruits are qualified for service, and if they possess the skills necessary for receiving training in a variety of military occupations.
The content of the test has been clearly laid out, but there is still a ton of information concerning the actual place where the test is administered and the time that is allocated for each section. The computerized test is administered in a “military entrance processing station” (MEP) or a satellite region that is identified as a “military entrance tests site” (MET). The difference in the two locations is that the METs are the places that are responsible for administering the written test, while MEPs are the places that administer the computerized tests.