5.1 Ignition switch
a) LOCK (Blocking): This is the only position in which you can remove the key from the ignition switch. This will block your vehicle's ignition system and transmission. If the steering wheel is locked, turn it slightly to the right and left and turn the ignition to the ACC position (Auxiliary consumers of electricity). If the steering wheel does not unlock, your vehicle needs service.
If the driver's door is opened while the ignition key is in the ignition, a gong will sound to remind you to remove the key from the ignition. Note: If you feel that the key is stuck in the ignition, make sure you are using the correct key and that it is fully inserted into the ignition. Turn the key manually only. Do not use any tools or apply excessive force to turn the key in the ignition switch. If the above steps do not help, contact your dealer.
b) ACC (Auxiliary consumers of electricity): In this position you can turn on your vehicle's auxiliary electrical consumers when the engine is not running. Long-term use of electrical equipment (for example, audio systems) in auxiliary power mode may cause battery discharge and engine starting problems. Do not leave the ignition key in the accessory power position or in the "ON" position for an extended period of time.
c) ON: The key returns to the ON position after you start the engine and release the key.
d) START (Starter operation): Starting the engine. After the engine starts, release the key. The ignition key will return to the ON position.
(The material was created based on information from the website chevyman.ru)