SSL on AWS Postgres RDS

I was reading this: http://docs.aws.amazon.com/AmazonRDS/latest/UserGuide/CHAP_PostgreSQL.html#PostgreSQL.Concepts.General.SSL Step 2 says "Install the certificate in your operating system", but I am able to connect with psql without doing anything, and when I do, it says SSL connection. Without the servers certificate, how can it do this? Where are public certificates to be kept for a client to check? I've seen things talking about ~/.postgresql, others saying with the rest in /etc/ssl, but I don't see Amazon's anywhere on my system.