Intransitive and transitive verb pairs
'The door opens' and 'someone opens the door' frame the event differently. Learn Japanese verb pairs together with their particles and the participants in the action.
A change versus an action on an object
ドアが開きました。 means 'The door opened.' 私がドアを開けました。 means 'I opened the door.' 開く（あく） describes the door's change, while 開ける（あける） describes an action performed on it.
An intransitive sentence does not mean that no person was involved. ドアが開いた focuses on the door opening; it does not by itself establish whether wind or a person caused it.
Learn pairs with their particles
電気が消える describes a light going out, while 電気を消す describes turning it off. 授業が始まる and 授業を始める similarly distinguish a lesson starting from someone starting a lesson.
Not every pair is formed through one predictable ending change. Learning 開く and 開ける does not justify changing every く to ける. Check actual pairs and examples in a dictionary.
Extend the contrast to states
電気が消えています。 describes the light being off. 電気を消しています。 can describe someone turning it off or keeping it off, depending on context. Changing the verb changes the focus as well.
Before practicing, decide whether you want to identify who acted or describe what happened to something. Then add the nouns and particles and describe the same event in two short sentences.
Check: Which says 'I closed the window': 窓が閉まりました or 私が窓を閉めました?
Show the answer and why
私が窓を閉めました。 identifies the speaker as the person who closed it. 窓が閉まりました focuses on the window closing without identifying who caused it.