To park a vehicle on flat terrain safely, it is essential to **turn off the engine and engage the parking brake**. This ensures that the vehicle does not move accidentally, as the parking brake is specifically designed to keep the vehicle stationary when parked.

- **Turn off the engine**: Stopping the engine is essential to avoid unnecessary fuel consumption and reduce the risk of the vehicle moving on its own.

- **Engage the parking brake**: This brake is a crucial safety measure that prevents the vehicle from moving, especially on flat surfaces where gravity does not help keep the vehicle in place.

In situations where the vehicle is parked on a slope, it is recommended to leave a gear engaged (first or reverse, depending on the direction of the slope) as an additional safety measure. However, on flat terrain, this measure is not necessary, and using the parking brake is sufficient to secure the vehicle.