I am trying to get my head around how to use the 'Ads'

I am trying to get my head around how to use the 'Ads' feature on Pro sites. I have activated the module and go into my settings to edit the ads. I have 2 levels of subscription - basic and pro (both are paid levels). Say for example I want an ad that says 'Test Ad' on the top of all Basic subscription sites - what settings do I need to have in place.