The ASVAB also known as the Armed Services Vocational Aptitude Battery is a test that measures your aptitude which is how well you do something.  A common mistake by most people is thinking that it is a measure of you IQ. Many people either forget this or don’t know this and they get worked up about the exam.  Saying that, it is also important to take a ASVAB sample test to insure you know what type of questions will be asked.    Another thing to keep in mind is every person in the armed forces has to take the exam and you are not being called out to take it. 
As a general rule of thumb, anything over an 85 on the ASVAB will qualify you for nearly any position in the armed forces. But there are slight breakdowns within each score. For example, in order to qualify for Surveillance and Communications (SC) in the Army, Word Knowledge, Paragraph Comprehension, Arithmetic Reasoning, Auto & Shop and Mechanical Comprehension all require high marks. Though scoring an 85 or above would guarantee you scored in a high enough percentile to qualify for SC.
In the 1950s, the military adopted a single exam known as the Armed Forces Qualification Test (AFQT). Used as a screening tool, the AFQT measured a recruit’s ability to absorb military training and their future potential. It was supplemented by service-specific battery tests for the purposes of MOS classification. In 1972, the Department of Defense determined that all services should use one exam for screening and assigning individuals to an MOS. The AFQT was phased out over a two-year period in favor of the current Armed Services Vocational Aptitude Battery (ASVAB) test.
With only a minute or two to answer each question, this part of the test might seem a little intimidating. But if you know how to approach the questions in this section, you should have no trouble at all. It’s well worth your time to take our practice tests, using the same logical steps to solve each problem until they become second nature. To solve these word problems, you will need to:
Another big advantage of practice tests is that they are fun. It’s fun to challenge yourself and see what you know. Instead of wondering if you are studying the right things or just wasting your valuable time, good practice tests can help you find out what you need to know while injecting your study time with excitement and competition as you try to outdo yourself each time you take a test.
Command over the U.S. Armed Forces is established in the Constitution. The sole power of command is vested in the President by Article II as Commander-in-Chief. The Constitution presumes the existence of "executive Departments" headed by "principal officers", whose appointment mechanism is provided for in the Appointments Clause. This allowance in the Constitution formed the basis for creation of the Department of Defense in 1947 by the National Security Act. The DoD is headed by the Secretary of Defense, who is a civilian and member of the Cabinet. The Defense Secretary is second in the U.S. Armed Forces chain of command, with the exception of the Coast Guard, which is under the Secretary of Homeland Security, and is just below the President and serves as the principal assistant to the President in all defense-related matters.[16] Together, the President and the Secretary of Defense comprise the National Command Authority, which by law is the ultimate lawful source of military orders.[17]
Military tactics concerns itself with the methods for engaging and defeating the enemy in direct combat. Military tactics are usually used by units over hours or days, and are focused on the specific, close proximity tasks and objectives of squadrons, companies, battalions, regiments, brigades, and divisions, and their naval and air force equivalents.[31]

You should note that the exam is given only in English. This is because all of the documents you will need to reference during your military career are in English. Even if English is not your native language, you should be able to make the cut as long as you study enough. You may need to take another test, the ECL (English Comprehension Level), to make sure that you can read and follow instructions given English if it is not your native language.
The Student ASVAB is the most flexible of the exams. It is typically provided to high school students to help them assess their skills, job prospects, potential military positions, or college majors. The ASVAB for students is essentially the same as the MET ASVAB exam, only students are not necessarily testing for positions within the military. The students’ school counselors examine their scores and help them decide on what to do after graduating from high school. This test is still an important component of a student’s education because it can help them identify their strengths and weaknesses and help set them on the right track for their future career goals.