about something that happened at any time in the past — not saying when exactly. It often comes at the end of sentence It means “in my life until now.” Example: I have eaten sushi before. (It happened once or more in my life.) I haven’t talked to a detective before. (It means this is my first time talking to a detective now.)
something happened earlier than we expected or is done before now. Example: I have already finished my homework. ( It’s done — maybe sooner than expected.) You have already asked that question. You have asked that question already. ( It means the question was asked earlier, no need to repeat.)
talk about something we expect. It often comes at the end of sentence. Note: We only use yet in question and negative sentences. Examples: Have you finished your homework yet? (question) I haven’t finished my homework yet. (negative) (I expected it to be finished, but it isn’t done.)