Go into edit mode on your hub and look in the top right hand column under "add content capsules", subheading "product". There you should see a button for Ebay and a button for Amazon. Click on the Amazon button and the ad is placed into your Hub. You can then edit the Amazon capsule to find the product you would like to advertise.
You can also mouse over the left hand side of the text body in edit mode and a floating button will come up that says "insert capsule". Position the button where you want the ad to be and click on the button. A list of capsule types will pop up, chose Amazon and edit the capsule for product preference.