Each publisher including you has a unique referral link that you can use at your ad space or elsewhere.
The link can be found in Admitad Extension in the "invite a friend" tab.
If a user follows this link and signs up to Admitad within a year after clicking on the link, he will become your referral, and you will receive a percentage of Admitad's profit from him. You will receive a percentage of the profits your friend brings to Admitad. Note that your reward is not withheld from the referrals' rewards, but is paid by Admitad itself, so your referrals do not lose anything.