Tracking purchases - Anyone knows how?

I want to create a website that tracks purchases hhmm kinda like affiliate links but not really. Here is a website that does that http://stratusmall.com they can know who among their hundreds of associates led the buyer to buy whatever.

So if I send someone to your site, and they click on "purchase now", your site will know it is me who sent them and check them out with my number.

Help are much appreciated, Thank you guys in advance.

You are talking about something like this:
http://replacementsticks.com/index.php?route=affiliate/login





pm me or if you have skype: bobby__boucher