Account activation, CodeIgniter - php

Question

I want to create an account activation where after registering, a link would be sent to an administrator (or one) email whereby the admin just has to click that link to activate that account.
I have the registration and login working. I'm using MySQL Workbench and have a "flag" or rather just a field in my accounts table (named user_login) to tell whether the account is enabled or disabled, which is disabled by default after registration.
I am stuck and sending a link through email, I'm not sure where to begin. That link that I want to send would contain a random string and would be sent to the admin, say abc/123/random?stringis=1234. Then the admin would just have to open his email and click on the string and then that specific user's account would be activated. I found this and this but that's just for how to send a link through email.
I don't have an idea on the logic. Do I create a function whereby the link would go directly to the function and from there, it would change the value in my table to enabled or whatever I call it so that the user's account is counted as activated? Do I need to create a new field to match the random generated string then?
Main idea is I'm trying to do like those typical sites whereby a link would be sent to the user to activate the account once he/she clicks it in the email, but this time just to a specific email which is the admin's.
EDIT:
In controller
public function activate_user($activation_code)
{
$result = $this->home_model->activate($activation_code);
if($result != FALSE)
{
echo "You have activated :".$result[0]->user_id.".";
}
else
{
echo "Activation failed, something went wrong.";
}
}
In Model:
public function activate($activation_link)
{
$this->db->select('*');
$this->db->from('user_login');
$this->db->where('activation_link', $activation_link);
$query = $this->db->get();
if($query->num_rows() == 1)
{
return $query->result();
}
else
{
return FALSE;
}
}

Answer 1

First
Database
add two column
activation_token{varchar|255}
activation_time{datetime}
After registration Success
add some randome has into activation_token(md5 or sha1(up to you))
add time if registration using Current timestamp(now())
Link
link should be
I strongly prefer userid in activation url
because it's remove the link duplication.
http://sitename.com/activation/{user_id}/{hash}
in controller
public function activation($user_id,$hash)
{
$timeOfexpiration = 3600;
$data = $this->model->get_data($id,$hash);
if(!$data)
{
return false
}
//if user found
//check expiration of linke
//like
if($data['activation_time']+$timeOfexpiration < now())
{
return true;
}
else
{
return false;
}
}

Answer 2

for that you need to add one more field in table called activation_linkwhen user register in site then generate random string and store that in activation_link and send link to the user so once user back then check the link and activate that user.