To save statistics using Adning you need to install the free add-on SmarTrack. You can do this by going to Adning in the admin menu, then select Add-Ons and install the smarTrack add-on.
If you did and still no stats are available something may have gone wrong during the smarTrack plugin activation. In that case go to your plugins page, deactivate the smarTrack plugin and reactivate it again. Now stats will be available for your banners.