The following information can be found in Section 3 of the USGA Handicap System manual:
In order to obtain a Handicap Index, a player must join a golf club and post adjusted gross scores. These scores are subject to peer review. After at least five scores have been posted, the club will be eligible to issue a Handicap Index to the player in accordance with the USGA Handicap System.
A USGA Handicap Index is one benefit of LGA Membership, which can be obtained by joining one of many LGA Member Clubs in the state. Please visit the Membership section of this web-site for more information.