After you choose your card design you are taken to the DESIGN tab of your event. In the EDIT DESIGN tab you can design your card and more.
As you can see on the left side of the image below you can add Logos and photos to your card. You can also choose the upload your own design.
If you do not like your chosen design you can also change the card design on the left side. This feature is used often when customers send multiple cards and dont want the cards to all look alike. Cards can be added using the +ADD symbol.