Select 
on the toolbar to activate it.
This navigation mode only works with digital terrain models (DTM). If you activate the Walk mode and there isn't any DTM in your scene, you will be prompted with the following window:
Navigation
- Left-click and drag to rotate your view
- W to move forward
- S to move backward
- A to strafe left
- D to strafe right
Gamepad Controller
You can use gamepad controllers (e.g., Xbox One controller) to rotate and move around in your scene. Simply plug in a controller and click the gamepad icon 
on the toolbar.
- Left stick to move around
- Right stick to rotate the camera
From the 
Navigation settings, you can adjust the walk speed, player height, right-stick sensitivity of the gamepad, and set walk boundaries.