The Card templates contain 'placeholder images, To replace, you can drag in a new image and drop it on the placeholder, or Copy the new image, click on the placeholder and paste.
The background artwork can be changed by selecting and deleting the existing artwork, then pasting in you own, resizing and repositioning to fit
All Text on the card templates is in Text Boxes or in Shapes. Most (in not all) is Placeholder text. Clicking on it and starting to type will immediately remove the Placeholder, and replace it with the entered text, set to the same style as the Placeholder. Any text that needs to be upside down on the page to be upright in the card is either not included on the templates or is placed in a text boc that has been rotated 180° If there is such text on the template, the box will rotate when you start entering text in it, and return to the upside-down rotation when you deselect the box.
Experiment. If you make an uncorrectable mess, close the document without saving, and open a new template to try again.
Regards,
Barry