You can select two background images for your card: one on the front and one on the back. Either one may be horizontal (landscape) or vertical (portrait). They don't have to match.

You switch between those two shapes by selecting the Horizontal or Vertical tabs above the image menus. The menus, at first, will be collapsed. You can expand any of them by clicking on its arrow button.

There are separate image menus for the front and the back of your card. That's because on almost every cover stock you can select there's a coating on the card front, but no coating on the card back: if you picked a glossy stock, the back would still have a matte finish. The full-color illustrations won't print with as much contrast on a matte stock. So in most cases the card back images are designed to work well even on uncoated paper.

Switch between the front and back of the card with the two tabs above the card preview, on the left side of the page.

You may want to start by browsing through most or even all of the background images. That will be a lot simpler if you start by turning all of the text areas off, so the text won't get in your way. You can turn them back on at any time.

When you swap between horizontal and vertical backgrounds, some of your text areas may no longer fit on the card - text that's low on a vertical card will be way down below the bottom of a horizontal one. If this happens the text position box will turn red, and your text will get moved until it's more or less in view. That may annoy you, but it's actually less annoying than it would be if your text disappeared completely. Trust me on this. I found out the hard way.