How to redirect from a page into another page when condition is true or false in Codeigniter?

Use the redirect() function from the URL Helper.
EDIT: load the url helper:
Example:-
$this->load->helper('url');
if (condition == TRUE) {
   redirect('new_page');
}
Example:-
Use redirect() helper function.

Example :

$this->load->helper('url');

if ($logged_in == FALSE)
{
     redirect('/login/form/', 'refresh');
}