The ASVAB test is taken by individuals interested in joining the U.S. military. It may be taken by high school students in the 10th, 11th or 12th grade. Or, it may be taken by someone who has earned a GED or higher degree. Along with determining your suitability for enlistment, the score you receive on this test lets officials know what military occupational specialties you may qualify for.
As of 2017, the U.S. spends about US$610 billion annually to fund its military forces and Overseas Contingency Operations. Put together, the U.S. constitutes roughly 40 percent of the world's military expenditures. The U.S. Armed Forces has significant capabilities in both defense and power projection due to its large budget, resulting in advanced and powerful technologies which enables a widespread deployment of the force around the world, including around 800 military bases outside the United States. The U.S. Air Force is the world's largest air force, the U.S. Navy is the world's largest navy by tonnage, and the U.S. Navy and the U.S. Marine Corps combined are the world's second largest air arm. In terms of size, the U.S. Coast Guard is the world's 12th largest naval force. 
You are tested in four critical areas — Arithmetic Reasoning, Word Knowledge, Paragraph Comprehension and Mathematics Knowledge (see below) — these scores count towards your Armed Forces Qualifying Test (AFQT) score. The AFQT score determines whether you’re qualified to enlist in the U.S. military. Your scores in the other areas of the ASVAB determine how qualified you are for certain military specialties. Score high, and your chances of getting the specialty/job you want increase. The better score you get, the better chance you have of pursuing the specialty or field that you desire.
The exam is not a “pass or fail” test. Your score in each area reflects your own unique abilities. Of course, you will want to study with the aim of doing your best so that you can qualify for a job that fits your skills and career interests. Your AFQT score is compared to the scores of other recruits in the 18-23 year age bracket to see how your potential measures up.