They are displayed horizontally, with slide numbers starting from one, but there are features in PowerPoint that allow the user to change the slide’s size and orientation.

To change your PowerPoint slideshow orientation from horizontal to portrait, you must access the "Slide Size" feature under the "Design" tab.

If you label images in PowerPoint, you might have noticed that it's difficult to change the size of the text label and the image at the same time, unless you know this quick trick.

You can change the size of a slide in your PowerPoint presentation through the "Design" menu on the Windows PC, Apple MacOS, and web-based apps.