To Steer: The Left and Right arrow keys or the "A" and "D" keys.
To Pedal: The space bar.
To Change Gear: Up and Down keys or "W" and "S" keys.
To Brake: You do not actually need brakes but if you feel safer, the Left "Alt" key.
To Change Views between Third Person and First Person (the rider): The "M" key.
The Horn: "C" key.
To Exit the program (not on the website version): Press the Escape key or click the "Quit" Button on the main menu.
You can change the default buttons on standalone installations (running the executable file, not on a website for Windows and Macintosh) in the configuration menu that appears before the game is run.