If you are a athlete hoping to play a sport in college, there are several things you MUST do.
Fill out the Clearinghouse Eligibility Form at www.eligibilitycenter.org; fee is ~$90 (waivers are available for those who qualify).
Take the SAT and/or ACT; use the code 9999 to send your scores to NCAA. Maintain a good GPA. Stay in contact with your counselor and coach to verify you are taking the required courses.