If you have added in your Amazon affiliate code to your account, everything is set up for your hubs.
However Amazon ads will NOT automatically be added to each hub, and you will need to add them each time.
It is a really straightforward process. Just as you add a text box or image to your hub, there is an option for an Amazon box. Just add in as many as you like, to the place you want them to appear in your hubs.
You get the option to have Amazon choose content to display, or you can specify items which you want to display.
Having Amazon choose for you will mean that you do not have to worry about items going out of stock or being discontinued, which will stop them from displaying. However you may want to display specific products. Its up to you.
Hope this helps!