There is more than one way to create an affiliate link on Zazzle. This covers one of the basic ways of doing so. Make sure you are logged into Zazzle and that you are signed up for the affiliate program (sorry that I can't explain how to do this, as I signed up a long time ago).
You can then paste this link where you want it, such as on facebook, Twitter, an email, etc. (To paste either press CTRL+V or right click with your mouse and choose Paste).
By the way...the url that you paste should look something like this. http://www.zazzle.com/cupcake_love_keychain-146881358322495734?rf=01230000000
The first numbers relate to the product you are referring. The ?rf= part tells Zazzle that someone is referring a product and the last numbers are your referral number. If you don't see the ?rf= followed by a string of numbers then you will not get a referral.