How to handle checkboxes

Thanks for the reply, I'm not sure I understand though. This is the part I'm having trouble with..

// attachments

$checked = $this->input->post('attachments');
if ($checked->nui == 1){
//echo 'Nui has been checked';
$this->email->attach('/attachments/somefile.pdf');
}

//

I dont know how to access the checkboxes correctly