The standard dimensions of a printed business card are 3.5 x 2 inches. That’s the finished card size.
Make the document page size equal to the card size plus the bleed area, or 3.75″ wide x 2.25″ high, to be trimmed down to the finished size after printing. If you aren’t planning to include bleeds, the bleed area isn’t necessary, so set the document size to the finished size, 3.5 x 2 inches.
If you’re designing a vertical card with the long size up, simply switch the page width and height so you won’t have to rotate the card to see the design the way you intend it.