Once you have purchased Spotlight Ads, you can apply them to any vehicle in your inventory. To do so, select a vehicle from your inventory list. Click the "Apply" link located in the Spotlight Ad column.
You can access your inventory from the following locations:
Vehicles > Inventory List
Vehicles > Vehicle Details > Advertising tab
Advertising Products > Spotlight Ads
The primary photo on the Vehicle Details page is the default photo for your Spotlight Ad. However, you have the option to select a different photo.