Hi, Leyi, and welcome to E-Learning Heroes! ✨
You can add the Previous/Next buttons to every slide at once, using the Slide properties in Story View. There, you can also set the slides to advance automatically or by user:
Take a look at this article for additional information:
For other buttons or features that you want to show in every slide, or to create layouts and a consistent look in your project, you can use Slide Masters. Below you will find some linked resources to learn about Slide Masters and how they can help you: