When you edit the slide master, all slides that are based on that master will contain those changes. The related layout masters appear just below the slide master (as in this picture from PowerPoint for macOS): The master slide is the top slide in the thumbnail pane on the left side of the window. To open Slide Master view, on the View tab, select Slide Master: When you want all your slides to contain the same fonts and images (such as logos), you can make those changes in one place-the Slide Master, and they'll be applied to all your slides.
