Present Perfect vs Past Simple

We use Past Simple when we know exactly or really care when the action happened:

• I was at work two months ago.
• My mother gave birth to me, when she was twenty two.
• At last I saw her yesterday.

But if we have such words like before, just, ever, never, already and yet, in this case we use Present Perfect.

• Have you ever been to Poland?
• She has never eaten oranges.
• I have just finished my work.
• He has not read this book before.
• I have already cooked the dinner.
• They have not finished their work yet.