Open your PowerPoint presentation
In the left thumbnail pane, select the slide you want to copy
Right-click the slide and choose Copy
Right-click where you want the copied slide to appear
Choose Paste
To copy a slide to another presentation, open both presentations
Copy the slide from the source presentation
Paste it into the destination presentation
You can also use Ctrl+C to copy and Ctrl+V to paste
On Mac, use Command+C to copy and Command+V to paste