Both “yet” and “already” are used with the present perfect.
Already is used in positive sentences.
Yet is used in questions and negative sentences.
Imagine that you and your friend are going to travel. There are many things to do, and you ask your friend if he has done these things:
Have you bought the tickets yet?
Have you arranged a taxi yet?
Have you reserved the hotel room yet?
Have you packed the bags yet?
In all the examples, use yet at the end of the question.
Positive and Negative Answers
Yes, I’ve already bought the tickets.
Yes, I’ve already arranged a taxi.
No, I haven’t reserved the room yet.
No, I haven’t packed the bags yet.
Use already in the positive answers, and yet in the negative answers.