There are many rules in place that limit when coaches are able to be in contact with student-athletes. There are different sets of rules for each level, including JUCO and NAIA.
Student-Athlete Guide for College Recruiting
Handbook that outlines the rules, requirements, and more for college-bound athletes.
In order to compete in NCAA division 1 & 2 sports, you must register with the NCAA Eligibility Center.
NCAA Future Student-Athlete Page
This website provides more information on the eligibility center, the different divisions, requirements, and more information on college sports in general.