Create custom url links in code igniter - mysql

Question

I have searched all over the internet for information that would help me achieve this seemingly simple thing.
But I can't get my hands on any that is helpful.
What I want to do is to create a custom url link like http://mywebsite.com/users/username,
where
1) 'users' is a MySQL table name
2) 'username' is a column name.
I did some digging on the internet and found this code on github:
<?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?