sessions

[eluser]ebuoe_007[/eluser]
i'm new to codeigniter and usually when when working with sessions i do create them when users log in to the site then i put a verification code on top of each page viewable by the user to ensure that the user is allowed to view the page and when the user log's out the session is destroyed but,going through CI documentation it said something like the session will be created automatically and expire on its own.

Q:how do i ensure the verification of users using session in CI.do i need to put verification code on each page like i used to ?