This article explains how to create greeting cards using Adobe Photoshop CC 2019 and later.
How to Make a Greeting Card Template Using Photoshop, Simple Photoshop Tutorial
To make a landscape card, you will need to create a document that is oriented portrait and then fold it in half. The image will be on the front, but the text will be on the inside, so you will need to run the paper through the printer twice. You can even add a logo and credit line to the back of the card.
Create a new document in Photoshop with the following settings:
If you don't see the rulers on the page, select View > Rulers to turn them on.