Become a member of the United States Chess Federation (USCF).
To join, just come to an SCA tournament that includes USCF-rated sections. You can buy a membership at the tournament or online at www.uschess.org

2.

Play in one of the SCA's USCF-rated tournaments. It takes just four rated
games to earn you a provisional USCF rating, so you can become rated
after just one tournament! Tournament schedule

Note: You don't have to play rated until grade 10. Some tournaments will offer new rated sections for younger players. But we'll always offer the regular non-rated sections in those same tournaments. Becoming rated is always optional for grades K-9.