Interrogative adverbs (soru zarfları) are used to ask questions about the circumstances of an action (how, when, where, why).

Common Interrogative Adverbs:

• Nasıl?: How?
  Example: Nasıl geldin? (How did you come?)
• Ne zaman?: When?
  Example: Ne zaman gideceksin? (When will you go?)
• Nerede?: Where? (location)
  Example: Nerede yaşıyorsun? (Where do you live?)
• Nereye?: Where to? (direction)
  Example: Nereye gidiyorsun? (Where are you going to?)
• Nereden?: From where? (origin)
  Example: Nereden geliyorsun? (Where are you coming from?)
• Niçin? / Neden?: Why?
  Example: Niçin ağlıyorsun? (Why are you crying?)
  Example: Neden söylemedin? (Why didn't you say?)
• Ne kadar?: How much? / How long? (quantity, duration, or degree)
  Example: Ne kadar bekledin? (How long did you wait?)
  Example: Ne kadar Türkçe biliyorsun? (How much Turkish do you know?)

These adverbs usually appear where the answer would naturally fit in the sentence, often before the verb.