On almost every page on Hubpages, go to the bottom of the page, the very very bottom where it says About Us, Blog Etc.
One of the options will be Link to This Page
Click that, and there you go, pick your tracker, copy the url and you are set. If the person who clicks that url (like a friend or whomever) within 30 days, you get credit for referring them.
You can create new referral tracks, and view the stats on your current ones in the earnings section (where you signed up and entered info to join the earnings program), then at the bottom of the list of options, referral trackers.