The university you are applying to will evaluate your SAT/ACT scores, GPA, the classes you've taken in high school, letters of recommendation from teachers and mentors, extracurricular activities, college interviews, and motivation letters/personal essays. The significance of test results varies from university to university.
In general, however, the higher you score on SAT/ACT, the higher is the chance that you will get into your dream school and qualify for government and university-sponsored scholarships.