Firstly, movement entirely depends on the headset. Some headsets have a joystick, some allow you to freely walk. Most people are ♥♥♥♥♥♥♥ broke though, so you probably have a joystick.
Press the large, green "PLAY" button to open the game. Make sure you're headset is properly connected to your PC and you also have SteamVR running.

Tilt the joystick on your controller to move. If you're rich and have a private room to move freely, start walking.

Why did you waste your valuable time? You could have spent your time actually playing the game! You could have spent your time going outside and/or reading a book! You could have spent your time playing Cars 2: The Video Game on your Xbox 360! But you instead decided to come here... Why?