"Yok" is usually used for you don't have things but these mean the same in some cases. For example; :"Gelmek ister misin?" ("Do you want to come") :"Hayır(yok), gelmek istemiyorum" ("No, I don't want to come") but(usually) :"Kalemin var mı?" ("Do you have pencil") :"Hayır, Kalemim yok" ("No, I don't have")

In the daily language, you can use "yok" or "yo" as the synonym for "hayır", if you mean "no"

"hayır" is from your language. We use it for the meaning "good deed", on the other hand, it means "no" in our language.

yok: 1there isn't, there aren't