What the person referring needs to do is either send out their link via their social networks, or they can email it. The person that receives it and clicks on their link (which are the parameters you set up in the campaign) will be lead back to your site. You can reward the friends that click on the link with a personal code by completing the section on the Reward setup page. So they click the link, and it takes them to the widget and they will see their personal discount code. Then once they convert on the page you can send the referrer their reward manually.