Row Level Security, in plain words

Row Level Security means: every read and write is checked against rules you wrote, row by row. With RLS on and no rules, nothing is readable — which is the safe place to start from.

Open the SQL Editor and add one rule: signed-in people may read notes.

$ create policy "signed-in can read notes"
$ on notes for select
$ to authenticated
$ using (true);
Success. No rows returned

• for select = this rule is about reading.
• to authenticated = it applies to signed-in people only.
• using (true) = once signed in, every row passes. Narrow this later to auth.uid() = user_id so people see only their own rows.