There are several ad programs on Hub Pages. One is the Hub Pages ads run and administered by Hubpages. Another is Adsense run by google. There are several others including Amazon and Ebay. The essense is that they occupy space on hub pages you right and you recieved a % of the revenue that is derived from people clicking on ads produced on your hub pages. They are a multitude of hubs and articles on this topic. I suggest you do a search and read a few hubs if you want to know more.