Creating a referral url

I need to create a referral url for every member of my site, something like this: http://mywebsite.com/ref/user, where user is a unique field in a database table. Please can someone give me a hint on how to go about this? I'll appreciate a dummy code, since I'm new to PHP and CodeIgniter.

I did some digging on the internet and found this code on github:

   

Code:

<?php
      //check for referal links
      function referal()
      {
       $CI =& get_instance();
       $cookie_value_set = $CI->input->cookie('_tm_ref', TRUE) ? $CI->input->cookie('_tm_ref', TRUE) : '';
      if ($CI->input->get('ref', TRUE) AND $cookie_value_set == '') {
        // referred user so set cookie to ref=username
         $cookie = array(
        'name'   => 'ref',
        'value'  => $CI->input->get('ref', TRUE),
        'expire' => '7776000',
      );
        $CI->input->set_cookie($cookie);
        return TRUE;
       }elseif ($cookie_value_set == '') {
         $cookie = array(
        'name'   => 'ref',
        'value'  => 'sso',
        'expire' => '15552000',
      );
        $CI->input->set_cookie($cookie);
        return TRUE;
    
       }elseif ($cookie_value_set != '') {
         //already referred so ignore
        return TRUE;
    
       }else{
          return TRUE;
       }
      }
    //end of hooks file
    ?>

The owner of the gist only mentioned saving the file as referral.php inside the **hook** folder. This is not helping me with what I want to achieve, I don't know how to use the code:
1. How do I pass the **referrer** field to the variable **username** from the **users** table?
2. How do I load the hook file to view (register.php)?
3. How and where do I call the hook file?

So can anybody give me an insight?