When you are considered a career in the military you need to take the ASVAB test. But each branch of the military has different ASVAB requirements that you need to meet. They are different levels of education that you must reach to take the test. But you also need to score a certain amount of points on that ASVAB test to gain access into the branch you desire.
To be admitted to the ASVAB testing room you will need to show a valid id. It is also important to be on time (or early!) since you will be turned away if you show up after the scheduled start time. The ASVAB can be given via computer or pencil and paper.  If you are testing at a MEPS site you will take it on a computer.  The pencil and paper version is given at most MET sites.  The computer version of the test is given as a "computer adaptive test" (CAT) which means that the test will adapt based on the level of the individual test taker (e.g., if you answer many questions correctly, you may be shown fewer questions).

One ASVAB sub-measure, the Armed Forces Qualification Test (AFQT)--which is just a separate analysis of the same tests that focuses only on four of the subtests--is also population-referenced, but its score from 1-99 is a percentile score. This means that if you score a 73, you scored as well as or higher than 73% of test-takers in the national sample.