In a nutshell, through affiliate links, coupons, and promo codes.
Clicking an affiliate link saves a cookie file in the user’s browser that allows Admitad Affiliate to track where the customer came from and who should receive rewards for it. Coupons usually contain the publisher’s ID, as well.
Promo codes are a bit more complicated: they tend to run free all across the Internet, making it hard to know who brought the customer in. Admitad Affiliate advertisers solve this problem by assigning unique promo codes to their publishers, so all sales made through particular codes are attributed to a specific platform.