Each slide layout contains placeholders for text, videos, pictures, charts, shapes, clip art, a background, and more, and they also contain the formatting, such as theme colors, fonts, and effects, for those objects.
Every theme (palette of colors, fonts, and special effects) you use in your presentation includes one slide master and a set of related layouts. If you use more than one theme in your presentation, you’ll have more than one slide master and multiple sets of layouts.
You change the slide layouts that are built in to PowerPoint in Slide Master View. The picture below shows the slide master and two of the ten layouts for the Basis theme in Slide Master View.
And then when you are laying out the content in your slides, you can pick the slide layouts that best suit your content, as shown here in Normal View.
The following diagram shows the various ‘parts’ of a layout that you can include on a PowerPoint slide.
More information about slide layouts