American colleges and universities consider a number of things about a student who wants to be admitted. A student' s interests and activities may play a part in getting accepted. But in most cases another consideration is how well the student did on college entrance exams. The SAT and the ACT are two of these tests most American schools accept.
ACT used to be short for American College Testing; SAT once meant Scholastic Aptitude Test. But today the letters no longer stand for anything. Most American colleges and universities require applicants for a bachelor's degree to take one of the tests. Some students take both.