When you add a new slide, you choose among different slide layouts that are based on your presentation’s theme.
Do one of the following:
Click 
in the toolbar, then select a slide layout.
Select a slide in the slide navigator, then press Return (or Option-click in the toolbar) to create another slide with the same layout.
After adding a slide, you can add your own content to it, including text, shapes, tables, charts, photos, and videos.
Select a slide in the slide navigator.
Press Command-D.
The duplicated slide appears immediately after the selected slide.
Open two presentations.
Select a slide in the slide navigator of one presentation, then drag it to the slide navigator of the other presentation.
Shift-click to select multiple adjacent slides, or Command-click to select multiple nonadjacent slides.
Select a slide in the slide navigator, then press Delete on your keyboard.
Shift-click to select multiple adjacent slides to delete, or Command-click to select multiple nonadjacent slides to delete.