There are different types of ads you can put in your hubs:
4. Ebay (if you already have a domain registered in your name)
In order to place ads, you first have to sign up with these affiliate programs. Signing up is easy and free, it just takes a few minutes. Step by step instructions on signing up with affiliates are provided in the Help section of HubPages.
Once you have signed up, each of the affilites will give you your unique member ID. You will have to enter this id in the affiliate settings on your account's page at HubPages. Once you have done that and the word "active" appears in front of the affiliates you have signed up for, you are good to go.
Finally, when you are making a hub you can choose to add Amazon capsules wherever you wish by adding the amazon option (available on the right hand side of the screen when you are organizing your hub). In this capsule you can choose specific products or let Amazon choose its own products according to the specific word you choose. Its easy and takes only a minute.
Google Ads appear themselves between the capsules and they are contextual (relevant to your context)
Kotera Ads can be turned "on" or "off" on individual hubs. The option is available when you are organizing the hub right on the top when you start. Just tick the box and Kontera Ads will start appearing. You can also change the affiliate settings by making changes on your affiliate settings page in your account at HubPages.
Hope this helps. Let me know. Good Luck