Many people shy away from working with Slide Masters because they think they’re too complicated. With the newer versions of PowerPoint, Slide Masters are a breeze.
From the View tab and the Presentation Views group, click on the Slide Master button. Before you start clicking, keep in mind that the slides on the left show all the layouts available to you: These are not your slides.
Want to make a change to affect all your slides? Scroll all the way up and change the first one. This is great for inserting a web address or a logo on every slide.