Every WEBKiosk has a few reserved spaces for advertisements. They all have a specific size and can be activated and deactivated. If you want to add an ad you just need to insert your advertisements HTML and JS code (from Google ads for example).
To do this go to "My WEBKiosk".
At your WEBKiosk click on "Tasks" and then "Ads".
You can then see the possible places for your ads. On the desired ad space click on "Tasks" and then on "Edit".
There you can insert your ad code and activate/deactivate the ad.