On Apple TV, we recommend an MFi game controller for the best experience, but you can also play with the Siri Remote.
With the game controller, Steer with the left stick, Accelerate with the right trigger, Brake with the left trigger, and Boost with the A button. You perform Stunts by moving the Left Stick and Right Stick in combinations (both up for example).
With the Siri Remote, make sure that you are holding the Remote sideways, with the touchpad on the right. Your vehicle auto-accelarates. Steer by tilting the remote left and right (like a steering wheel). To Boost, press the Select button (click the touchpad). To Brake, lightly touch the bottom of the touchpad. To Stunt, press the Play / Pause button; the game will automatically pick the best stunt for you based on how much time you have before you hit the water.