Character Cards are a special reward you can earn from Star Boxes.
These go into a special scrapbook you can access by tapping the Estate on Orchid Island.
Collecting sets of Character Cards allows you to unlock new information about Virginia, Sam, Jack, and all of your favorite June's Journey characters. This is a somewhat advanced feature that develops slowly over a long time, so we're not going to spoil the surprises here. Enjoy the stories!