Most of you would know that you can insert slides from another presentation by using the Slides from files menu option in the Insert menu. This is yet another way to do the same.

Open the presentations you want to copy/move slides to and from. Click Slide Sorter on the View menu. On the Window menu, click Arrange All to display both presentations. Click the slide you want to move, and drag it to the other presentation. If you want to copy the slide across then hold down Ctrl as you drag the slide.

Note: To select more than one slide, press Ctrl while you click.