Open your PowerPoint presentation
Go to the slide thumbnail pane on the left
Click the slide where you want the new slide to appear after
Select the Home tab
Click New Slide
Choose a slide layout if needed
To insert a slide in a specific position, right-click a slide thumbnail
Select New Slide from the menu
To duplicate an existing slide, right-click the slide thumbnail
Select Duplicate Slide
To insert a slide from another presentation, open the target presentation
Copy the slide you want
Paste it into the desired location in the current presentation