ca-pub-4564131316846146453456 (Note this is a made up random number) copy your affiliate code for latter use.
On HubPages.com click your 'UserName' top right of any page on HubPages then 'My Account'
then the 'Earnings' tab. Under the 'External Affiliate Settings' section click on the 'Configure' button next to where it says 'Google AdSense'.
You will enter the code you previously copied from your AdSense account. At this point I can't explain it in detail as I've already completed this step. But it shouldn't be too hard to complete the process from this point.
I hope this answer was helpful to you.