1. First you have to sign up for the Google AdSense program at http://google.com/adsense (make sure you read Google's Term of Service)
2. Log into your Hubpages account and click "My Account -> Affiliate Settings". Details here: http://hubpages.com/guide/before_first_hub/managin...
3. Put in your Google Affiliate Code. More detailed instructions with pictures here http://hubpages.com/help/googleadsense as to where to find your Affiliate Code.
4. Click the Apply Changes button.
5. To see how much money you are making on Google Adsense, log into adsense and look at their reports.