Controlling door locks using the key in the driver's door lock (Opel Corsa C)

Unlocking

Turn the key forward in the lock until it stops. Turn the key back to the vertical position and remove it.

Locking

With the driver's door closed, turn the key back to the stop, turn the key back to the vertical position and remove it.

Text copied from an online resource [opelbook.ru]

If the central locking device fails, the remaining doors can be opened or closed by pulling or pressing the internal locking device, respectively (impossible if the anti-theft device was previously enabled).