Newbie question

I'm a complete newbie and going through the CodeIgniter tutorial at this link.

https://www.codeigniter.com/user_guide/t...pages.html

When I get to the section "Adding logic to the controller, I don't understand what to do when it says "In order to load those pages, you’ll have to check whether the requested page actually exists:"  What am I supposed to do with the code below which is pasted below? Am I supposed to put it in the controller that I created just few lines above? 

application/controllers/Pages.php

public function view($page = 'home')
{
        if ( ! file_exists(APPPATH.'views/pages/'.$page.'.php'))
        {
                // Whoops, we don't have a page for that!
                show_404();
        }

        $data['title'] = ucfirst($page); // Capitalize the first letter

        $this->load->view('templates/header', $data);
        $this->load->view('pages/'.$page, $data);
        $this->load->view('templates/footer', $data);
}