In step one on this page it says to add select on sequence. Being relatively new to Postgres, what is a sequence and why does it need separate permissions and why is there what looks like an extra table for the sequence I didn't create?
-- run this in psql using the database created
-- in the previous tutorial
create role todo_user nologin;
grant todo_user to authenticator;
grant usage on schema api to todo_user;
grant all on api.todos to todo_user;
grant usage, select on sequence api.todos_id_seq to todo_user;