添加会话以登录Codeigniter

I have my simple login form. What will i do to put a session to it. here are my codes. I cant implement the tutorials in google. can someone please help me? Thanks!!

Controller:

function login_user(){
  $user_login=array(    
  'username'=>$this->input->post('username'),
  'password'=>$this->input->post('password') 
    );
    $data=$this->Infoserbilis_model->login_user($user_login['username'],$user_login['password']);
      if($data)
      {
        redirect('Infoserbilis/admin_page', 'refresh');
      }
      else{  
        echo '<script>alert("Invalid Username or Password");</script>';
        redirect('Infoserbilis/index', 'refresh');
 }
}

Thank you very much in advance for answering.

Try This for creating session for your code in if($data):

$session_data['logged_in'] = TRUE;
$this->session->set_userdata($session_data);

And Check session to logged status:

if (!isset($this->session->userdata['logged_in'])) {
      redirect(YOUR_LOGIN_PAGE);
}

try this code. Here is all possible solution and set session as username

also you can redirect and set message.

also make sure the session library is include for example

// Load session library
        $this->load->library('session');

Add session code

if ($data== TRUE) {
    $this->session->set_userdata('logged_in', $this->input->post('username'));
    //$data['message_display'] = 'Registration Successfully !';
    //$this->load->view('user/signin', $data);
    //$view="dashboard/profile";
    redirect('/UserDashboard');
}
else{
    $data['message_display'] = 'Invalid Email & Password';
    //$this->load->view('user/signup', $data);
    $view="user/signin";
}

for check user is log in or not then used this code

 if ($this->session->userdata('logged_in') == TRUE)
     {
         redirect('UserDashboard/');
     }else
     {
       redirect('login/');
     }

for more details about session library then read CodeIgniter Manual