Use the arrow keys to move, and WASD to rotate the camera, and press R and T to rotate the domino. When you are done, press Enter, then click to shoot a cube at the dominos. Domino Simulator requires the Unity Web Player, so it won't work on Google Chrome.
You can find the source code and an offline version where you can save your progress on the itch.io page:
Unity Web Player | Domino Simulator