Like the SAT, the ACT is a college-entrance-type exam. All 4-year colleges and Universities accept the results of the ACT for a student applying for admission.
The ACT tests 4 subjects; English, Reading, Math and Science Reasoning (there is a separate Writing Test that is optional, though students should probably take it). ACT scores range from 1 to 36 on both subscores and composite (average) score.
New in 2020/2021 for ACT- once you have taken a full ACT exam, you can choose to retake individual sections (English, Reading, Math, Science) in a future test. You no longer have to retake the whole test in order to try to boost one section's score.
See www.collegedata.com for average SAT and ACT scores for admitted students to your desired college or university.
Students wishing to register for the ACT may do so at http://www.actstudent.org/
HERE is a handy ACT to SAT conversion chart to help you see how your scores compare across tests.
Students needing a fee-waiver for the ACT can get one from their School Counselor. A description of Fee Waiver eligibility can be found here.