help with boolean

[eluser]KrizzAngel[/eluser]
im really confused. i know im a noob XD anyways can u guys help me with this:

function checker()
{
$is_logged_in = $this->session->userdata('is_logged_in');
if(!isset($is_logged_in) || $is_logged_in != true)
{
return true;
}

}

i made that function but i dont know how to use it to my index() and other page lol.. what i want to happen is if a user try to access certain page it will redirect to login(home page) if user is not logged in and on the other hand i dont want to access home page if the user is still logged in.