NCAA - www.ncaa.org
NAIA - www.playnaia.org
You need to register with one or both of these institutions in order to be eligible to play sports in college. You will find eligibility criteria as well as a list of schools that use a particular registry (i.e., either NAIA or NCAA). You can also see a list of showcase tournaments for NAIA for greater recruiting opportunities within the NAIA schools, rules on letters of intent, signing dates, etc. for both NCAA and NAIA.