Open an image you want to use for a greeting card. This should be a flat image. (i.e. use a JPG image or a flat Photoshop file with only a background layer.)
On the Create Cards panel, click the button for the card style you want.
The Action will stop prompting you with the crop tool. Drag the crop lines to trim the image the way you want it to appear on the card.
Commit the crop and the action will continue.
When the action is complete you will have a layered greeting card file called My Greeting Card. I suggest that you immediately save the file using File > Save As… and give it a meaningful name.
You may also want to modify the font to select a phrase and font style that matches the card design that you envision.