This only makes sense if the file has been zoomed. A new cursor with a hand appears. You can now drag left or right to interactively slide to the portion of the sound file you want to see on-screen. A position bar at the top of the graphical window shows the relative position of the display with respect to the complete file and also shows the current selection, if any exists.
The Scroll command can also be activated by clicking on 
in the toolbar section.