Create a login role

CREATE ROLE my_user LOGIN PASSWORD 'my_password';

Grant access to database

GRANT CONNECT ON DATABASE my_db TO my_user;

Granting basic read/write

GRANT pg_read_all_data TO my_user;
GRANT pg_write_all_data TO my_user;

Granting access to a schema in a db

GRANT USAGE ON SCHEMA public TO my_user;

Change DB owner

ALTER DATABASE name OWNER TO new_owner;