The Walk and Look controls work especially well when used in conjunction with each other. The controls only function when in Perspective mode. If you are in Orthographic mode, when you click either control, the camera automatically switches to Perspective mode.
Before proceeding with the following steps, right-click the wheel and select Options. Clear the checkmark next to Walk Tool - Constrain movement to ground plane. Click OK.
The walk speed is proportional to the cursor distance from walk origin indicator.