this

Used to refer to a person or thing that is near the speaker or is being shown or introduced.

• This is my friend Ayşe from work.
  Bu, iş yerinden arkadaşım Ayşe.
• What's this? It looks like a key.
  Bu ne? Anahtara benziyor.

Used to refer to something that has just been said or is going to be said.

• Listen to this: we won the competition!
  Şunu dinle: yarışmayı kazandık!
• Is this what you wanted to tell me?
  Bana söylemek istediğin bu muydu?

Used on the phone to say who is speaking.

• Hi, this is Elif from the dentist's office.
  Merhaba, ben diş hekimi muayenehanesinden Elif.
• Hello, this is Can, is Selin there?
  Alo, ben Can, Selin orada mı?