When you move the mouse cursor across the slide, an icon will appear in the lower left-hand corner of the window. Clicking that icon reveals a dialog box which allows you another means of moving forward and backward in the presentation (or ending it altogether) and selecting which slide you wish to view. You can also select a colored "pen" that allows you to make marks on the slide. This is especially useful for instructors who wish to highlight certain elements on the slide presentation. You can leave the pen "selected" as you move from slide to slide using the space-bar.