The phrase "to release the brake" means to let go or remove the device that stops something from moving. It is used to describe the action of freeing or allowing movement to occur. Full definition
Essentially, the vehicle's engine shuts off when the driver stops for a traffic light, for example, and starts when the driver releases the brake pedal. (articles.orlandosentinel.com)
The engine will turn back on upon the driver releasing the brake pedal. (gmauthority.com)
The launch control is as simple as traction control off, sport mode on, step on the brake and throttle at the same time, then release the brake. (motoring.com.au)