The Zoom/Pan selection allows you to set option about the Speed and look of Zoom/Pan features.
Pan Speed - Mouse and Keyboard sets the speed panning occurs at.
Zoom Speed - Mouse and Keyboard sets the speed zooming occurs at.
To pan with the mouse, simply click and hold the right mouse button while dragging the page. The middle mouse button, if your mouse has one, will allow for rapid panning in the same manner as the right-click pan option.