To insert a header or footer in PowerPoint:

1. In the View tab, select the Slide Master slide from the column in the left-hand side.
2. At the bottom of the slide, select the Layout icon.
3. Click on either Header and Footer or Slide Number, which will open a dialogue box.
4. From this box, you can add a Header, Footer, or Slide Number to your slides.
5. To not have a header on one or more slides, select the Don’t show on title slide option.
6. Once you are happy with your selection, click Apply.