Present perfect and past simple ("I have done" and "I did"): - She's looking for her bag. She can't find it. She HAS LOST her bag. (present perfect) This means that she doesn't have her bag now. The present perfect (something HAS HAPPENED) is a present tense. It always tells us about the situation NOW. 'She HAS LOST her bag' = She doesn't have her bag NOW. - She has found her bag. She has it now. Has she lost her bag? No, she has found it. Did she lost her bag? Yes, she did. She LOST her bag (past simple: a finished past event) but now she HAS FOUND it. (present perfect)

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Hello Suha, The past simple tense refers to an action that terminated completely in the past. Even if the action ended in the near past ,but it is marked by a full termination with no extension in the present. "He finished school last year." ( He is not studying at school anymore) " She was here 2 hours ago." ( She is not here now anymore) "He left one minute ago." ( One minute ago ( past) he was here ,now he is not here anymore ) The present perfect tense on the other hand refers to an action that expands over 2 time spans. It starts somewhere in the near past and extends to the present moment. It can't be a full past tense action because that one terminates in the past and it can't be a present tense action because that one happens in the present time without any association with a previous time. "He has just finished writing the letter." The action of writing started already in the past ( it might be an hour ago or minutes ago) and extended to the very present moment when this statement is told. He might be putting his pen down, thus the completion of the action extends to the present. If you said " he finished writing the letter " the action will have terminated in the past ,even if this past is an hour ago or minutes ago, but there are no traces of the action at this moment ( The letter might be already inside an envelope for example, when this statement is said). " Have you seen him lately?" "Lately" means in the recent past and it refers to the extension of the action into the present time. You could have seen him yesterday , today in the morning , a few minutes ago or right now . The time span extends from the near past to the "now" moment. I hope the difference is clear :)

I can find any better answer than learner, I agree with learner.