Advance PHP knowledge is needed to understand this technique
When advertising on a site, you want to know how the user actions from that site (if it converted or not: signed up or buy).
One solution is to add a domain.tld/?refer=somecode but that looks ugly for the ones who visit.
For fav20 I see if user registered by using the following code:
$referer = ‘domain.tld’;
setcookie(“referer”, $referer, time() + 3600 * 24 * 30,”/”);
And then I use the $referer variable to add it to a hidden field in the sign-up form and insert it in the database. User will be tracked for 30 days on my example.