From the slide-sorter view, select the slide you'd like to move. You can also press the Shift key to select a sequence of slides, or use the Ctrl key to select multiple, non-sequential slides.
After you've selected slides, you can copy them by right-clicking the slide(s) in the slide-sorter view and selecting Copy slide. Next, right-click the area in the slide-sorter view where you'd like to paste your slides and select Paste slide.