Past Simple: WHEN sth. happened is important Present Perfect: RESULT is important
- puts emphasis on the result -> Example: She has written five letters so far.
- action that is still going on -> Example: School has not started yet.
- action that stopped recently -> Example: She has cooked dinner.
- finished action that has an influence on the present -> Example: I have lost my key.
- action that has taken place once, never or several times before the moment of speaking -> Example: I have never been to Australia.
Signal Words of Present Perfect
already, ever, just, never, not yet, so far, till now, up to now