How to create an updatable view

Could anybody please help me make this view updatable. Im really strugling with it.

CREATE or replace VIEW user_notifications AS
SELECT u.user_id,n.heading,n.info,n.date,n.link,n.id,
False as seen
FROM users u,notifications n;

CREATE or replace VIEW user_notifications AS
SELECT u.user_id,n.heading,n.info,n.date,n.link,n.id,
False as seen
FROM users u,notifications n;