Present Perfect: Already, Yet, Just

• Yet: Primarily used in negatives and questions. It implies an expectation that something will happen or should have happened by now. It focuses on the unrealized potential or the absence of an expected event up to the present.
• He hasn't called me yet. (I expected him to call; the call is pending.)
• Have you completed the report yet? (I expect the report to be completed; is it done?)

• Still: Typically used in positive and negative statements. It emphasizes the continuation of a state or action, or that something continues to be true, often despite expectation or a passage of time. In negative contexts, still indicates a continuation of a negative state.
• He still hasn't called me. (He has continued not to call me; it's a prolonged absence of a call.)
• The store is still closed. (It continues to be closed, perhaps longer than expected.)
• Placement of still is generally before the main verb or after the auxiliary verb be. In still hasn't called, still precedes hasn't (or more accurately, still precedes the auxiliary verb, and not follows it).

Yes, already can be used in questions, typically to express surprise that something has happened or to confirm an expected event. For example, Have you already finished the entire book? That was fast! or Has the train already left? It indicates the speaker thought the action might still be pending.

Absolutely. I have just eaten uses the Present Perfect with just to emphasize the recency of the action and its current relevance (e.g., I'm not hungry now). The exact time is not specified. I ate ten minutes ago uses the Simple Past because ten minutes ago is a specific, definite past time marker. While both convey recent eating, the grammatical structures communicate different emphases: relevance now vs. a precise point in the past.

In very formal, literary, or archaic English, yet can sometimes be used in positive sentences with a meaning similar to still or even now. For example, There is hope yet. However, for B1 learners and in contemporary everyday English, yet should be restricted to negative statements and questions.

Still haven't emphasizes the continuation of a negative state or non-completion, often implying a sense of patience wearing thin or continued expectation. For example, I still haven't received my package suggests a prolonged wait. Haven't yet simply states that something has not occurred up to the present moment, maintaining a neutral or expectant tone without necessarily implying extended duration or frustration. For example, I haven't received my package yet states the current status.

The safest and most common placement for just and already is between the auxiliary verb (have/has) and the past participle. For example, I have just seen that movie. or She has already sent the email. Yet is almost always at the end of the sentence.