Standardized tests play a significant role in the college admissions process for most, but not all*, colleges. Before going any further, it's important to remember that far and away the most important factor in college admission is a student's strenght of schedule and how they've performed in that schedule. In other words, have you taken appropriately challenging classes and how have you done in those classes? This outweighs your test scores - whatever they might be.
Colleges use these tests as a basis for comparison. It's difficult enough to compare students from one high school, let alone trying to make judgements on a large number of students from across the country. What's to say that a Clarence studnet's 92 GPA isn't the equivalent of an 89 at another school? Or a 95 at another? That doen't even take into account schools that have entirely different grading scales. Although imperfect, standardized tests can provide a consistent reference point for all students.
There are two main standardized tests used in the admissions process: the SAT and the ACT. Although they are different tests, colleges accept them equally - they don't care which one you take. In fact, most colleges will only use the higher test score. We stronly encourage students to take both. Many students score higher on one test than the other. It's difficult to predict which one you'll do better on, so take both.
*There are nealy a thousand colleges that are test optional or test flexible. These schools de-emphasize or eliminate the roll of standardized tests in admission. There are some students who just aren't great test takers. Their score on the SAT or ACT just doesn't match their consistent, daily performance in school. If you fall into that category, then test optional schools might make sense for you. Talk to your counselor if you have questions about going this route. A full list can be found at https://www.fairtest.org.