Using pagination

That's correct. You can fecth some things automatic, but some you need to pass along in the $data array.

You need to change your model to accept an offset. It dosen't know you want 20 iterations.

In case you get stuck and want to cheat.

PHP Code:

// Controller
public function page() {
    $this->load->library('pagination');
    $config['base_url'] = base_url('admin/ads/page');
    $config['total_rows'] = $this->db->count_all('ads');
    $config['per_page'] = 50;
    $config['uri_segment'] = 4; // You may need to change this into 3
    $this->pagination->initialize($config);
    
    // You need to change segment(4,1) so it's matching the same number as uri_segment, in your case 3
    $offset = (intval($this->uri->segment(4,1))*$config['per_page'])-$config['per_page'];
    
    $this->data['ads'] = $this->ads_model->get_all_ads($config['per_page'],$offset);
    $this->load->view('admin/ads/list',$this->data);
}

// Model
public function get_all_ads($limit,$offset) {
    $this->db->order_by('company', 'ASC');
    $query = $this->db->get('ads',$limit,$offset);
    return $query->result();
}

// application/config/pagination.php - Default setttings
<?php
defined('BASEPATH') OR exit('No direct script access allowed');

$config['use_page_numbers'] = TRUE;
$config['full_tag_open'] = '<nav aria-label="Page navigation"><ul class="pagination">';
$config['full_tag_close'] = '</ul></nav>';
$config['prev_link'] = 'Prev.';
$config['next_link'] = 'Next';
$config['first_link'] = FALSE;
$config['last_link'] = FALSE;

$config['next_tag_open'] = '<li>';
$config['next_tag_close'] = '</li>';

$config['prev_tag_open'] = '<li>';
$config['prev_tag_close'] = '</li>';

$config['cur_tag_open'] = '<li><span>';
$config['cur_tag_close'] = '</span></li>';

$config['num_tag_open'] = '<li>';
$config['num_tag_close'] = '</li>';
$config['num_links'] = 4;