The slide master is a special slide that contains the layout, theme, and placeholders for your presentation.

To access the slide master, you can either press ALT + W + M or click on the view tab and then click on slide master.

It controls the appearance and formatting of all the slides in your presentation, such as the font, colour, background, and logos, and the footer.

You can use the slide master to make global changes to your presentation, such as adding a watermark, changing the alignment, or applying a new theme.

You can also create multiple slide masters for different sections of your presentation.

The slide master can help you save time and ensure consistency in your presentation.