A Slide Layout serves as a template for a slide. All placeholders on the slide layout “shows through” on a slide created with it and formatting choices made on the slide layout are inherited by the slide.
Every slide in a presentation is based on a Slide Layout. As such, you have to specify which slide layout from which slide master to use when you create a new slide. The slide’s appearance is determined by the Slide Master and Slide Layout and the properties found in them, as shown in the diagram below.