Before college, a student must obtain a high school diploma or its equivalent. What constitutes a high school equivalency varies by states but generally involves a standardized form of testing to ensure competency. High school generally requires four years of each basic subject--English, history, math and science--as well as a certain number of foreign language credits.
Although the minimum grade point average varies by school, the common factor is that every school has a minimum grade point average it will accept. Be aware of this when figuring out college options or, even better, throughout high school. You will want to maintain the highest grade point average possible so you will be sure to meet your school of choice's minimum requirement.
The SAT and ACT are standardized tests meant to show how well you should perform in a college environment. As a minimum entry requirement, all colleges require potential students to take at least one. Depending on the college, they may require a specific test or accept either. Generally, students can take both, multiple times if necessary, and colleges will accept the best score.