You can control your horizontal movement with the standard WASD control system.
Hold RMB (right mouse button) and move the mouse to turn your view, when the mouse is within the window
Hold MMB (middle mouse button) and move the mouse to pan your view
Roll the MMB Wheel (middle mouse button wheel) to move your view forwards and backwards
Hold SHIFT to double the speed of your viewport movements
The dialog box indicated is used to increase and decrease the movement speed of all movements you make in the main perspective viewport.