Previously, the monkey was trained to play the game with a joystick. During that process, a Neuralink device was connected to the monkey's brain and collected training data. That training data was then used to understand the monkey's intent in a later trial with the joystick unplugged. In that trial all movement on the screen was controlled exclusively by brain signals interpreted by the Neuralink device.
Later versions will be able to shunt signals from Neuralinks in brain to Neuralinks in body motor/sensory neuron clusters, thus enabling, for example, paraplegics to walk again. The device is implanted flush with skull & charges wirelessly, so you look & feel totally normal