That tab is for once you have set up your referral tracker. Click on the affiliate tab at the bottom if you haven't already and sign up. Then when you promote hubpages outside on the net with your tracker link and get sign ups - you then make money from the people you sign up (if they write and make money themselves of course).
You can use the "link to this page" button to link to any HP page. I use it to link to the sign up page - my own hubs - and also other excellent hubs.