title: How to track sells you make by visitors referred by another website?
body: <p>In my future website, I'll have partners and I want them to receive a certain percentage of money according to how much the visitors they sent me bought items.</p>
  
  <p>So this is a simple question:</p>
  
  <p><strong>How to know where the visitor comes from when he decide to purchase a thing on my website so I give the correct amount to the partner who referred the member?</strong></p>
  
  <p>(i use the php Symfony framework, I guess it has nothing to do with, but anyhow... ;D )</p>