Kapı kapatıldı.
English: The door was closed.
The passive voice in Turkish (-edilgen çatı) is used when the subject of the sentence is not doing the action, but is affected by it. The action is done by someone else, or the doer is not mentioned.
Use the passive voice in Turkish when you want to focus on the action or the object, not the person doing it. It's common in news, instructions, and when the doer is unknown or unimportant.
Kapı kapatıldı.
English: The door was closed.
Mektup yazıldı.
English: The letter was written.
Çocuklar okula götürüldü.
English: The children were taken to school.
Yemek hazırlandı.
English: The food was prepared.
Soru cevaplandı.
English: The question was answered.