SAT: The SAT is a standardized test that colleges use in their admissions decisions. The ETS (educational testing service) develops and administers the SAT tests. There are 3 sections on this test. There is a critical reading section, a math section, and a writing section that also consists of an essay. The scores for each of those three sections are scored from 200 to 800. So your SAT score would range from 600-2400. The average score for each section is around 500. The time it takes to complete the SAT is 3 hours and 45 minutes with breaks in between. Including the writing section, the SAT has 10 sections, but one of the sections is not scored. There is a penalty for guessing on the SAT.
ACT: The ACT is another standardized test that colleges use in their admission decisions. The ACT is scored on a composite scale out of 36. The ACT has 4 sections: a English section, math section, reading section, and a science section. There is also a optional writing section. Each section is scored from a 1 to 36. The composite score is simply the average of all the sections. On the ACT there is no penalty for guessing so it is to your advantage to answer every single question for the best score.
Some colleges want the ACT score, others want the SAT score, and some even want both. It is to your advantage to take both the SAT and the ACT and do well on both. Doing so will open up many scholarship opportunities. Also, do not stress over these tests too much. Colleges will also look at your transcript, recommendation letters, extracurricular activities, and your essay. But however, doing well on the ACT and the SAT will definitely help you in the college admissions process.