A banner is an image you can upload for your affiliates to use when promoting your program. When it is clicked, it will lead to your site and the visit will be tracked the same way visits from affiliated links are tracked.
To add banners, go to the Banners page and click the Add New button. Choose an image file to upload and optionally select category, specific URL for the banner to lead to, width and height.
From Settings -> Banners Settings you can add custom text, which will be visible in the Banners page of your affiliates' panels, and create categories for easier sorting.