High school athletes should register for the NCAA Eligibility Center at the beginning of their junior year. However, everyone has a different recruiting experience, so some might register earlier, some later. Ultimately, only athletes who are going to compete at the Division 1 and 2 levels need to register with the NCAA Eligibility Center.
When you do register, a college coach will need to ask that your profile be placed on the Institutional Request List (IRL). College coaches use the NCAA Eligibility Center to verify your academics and your amateurism. Only when a coach does this will your information be processed. Also, until you register with the Eligibility Center, you will not be allowed to go on official visits to schools or receive official scholarship offers.