Simple :
First, load this library
$this->load->library('session');
Then, to add some informations in session :
$newdata = array(
'username' => 'johndoe',
'email' => 'johndoe@some-site.com',
'logged_in' => TRUE
);
$this->session->set_userdata($newdata);
Next, if you want to get values :
$session_id = $this->session->userdata('session_id');
And to remove :
$this->session->unset_userdata('some_name');
A simple search "codeigniter session" could have help you ...
https://www.codeigniter.com/user_guide/libraries/sessions.html
Don't forget to upvote and mark as solved if you find this useful :)