Once you have created an affiliate link with your referral ID you can add a tracking code to it too. The tracking code will make it so if something you refer sells you can know where that sale came from.
You can make the tracking code be anything that you want, so you have your own unique identifier. For example, if you want to see if posting referrals on facebook works for you (what works well for one person may not for another), then you could just use the letters "fb" to mean facebook.
All you need to do is add &tc= to the url with your affilate ID plus whatever you want your tracking code to be after that equal sign. Like so:
And as mentioned I could make the tracking code be anything. So here's another example:
If you make up several tracking ID's you might want to write them down so you can remember them all, what they mean (if you use abbreviations such as "fb" for facebook or if you make up a special "code" that only you would know what it means).
So if something you referred does sell, where do you find out that info? Well go into your account and click on the Referral History link. Underneath the Name of the product that sold and the numbers underneath that it will say "TC:" and then the code you made up. If the referral came from a link that did not have a tracking code then nothing will be underneath the numbers. (Thanks to A_Plus_Products for the screenshot.)