To add a border to a PowerPoint slide, follow these steps:Open the PowerPoint presentation and go to the slide where you want to add the border.Click on the slide to select it.Go to the 'Design' tab in the ribbon and click the 'Page Borders' button in the 'Page Background' group.In the 'Page Borders' window, select the desired border options, such as the style, color, and thickness of the border.Click 'OK' to apply the border to the slide.