To find the code look in Assets->Standard Assets->Scripts
The game is meant to be played on Oculus devices, and although it works with keyboard and mouse, it is a terrible way of controlling the game
In the top menu bar of the Unity editor, select the "Game" dropdown and then select one of the options to change the input devices

Hold either hand-grip button to move towards where your hand is facing
Move either thumstick up or down to control your length
Press either thumstick inward to change the camera orientation
Press the A, B, X, or Y button or either trigger to access the menu

Hold the w key to move towards where the camera is looking
Hold the left mouse button to grow
Hold the right mouse button to shrink
Hold the spacebar to change the camera orientation
Press the r key to reset the level
Hold the Escape key to access the menu