Postgres SQL on AWS RDS how to grant permission for schema, select on tables to user

I have logged in as superuser and created a readonly user. When I run grant command, it says that schema does not exists I am logging in as root: sql -h myhost_name -U root -d postgres -W grant usage on schema autorsid to readonly ; ERROR: schema "autorsid" does not exist while schema does exists but schema owner is not root. Isn't when you are superuser, we should be able to grant permissions for all database/schema/tables etc.