1. When something happened and it is NOT important when (past simple?)
2. When something happened in the past and is still going on (I have lived in London since 2017)
3. When something happened in the past and you can see the results now (She has painted the walls)
4. When something has just happened or hasn't happened yet (I have just called her. I haven't received an answer yet.) (signal words: just, yet, lately, recently)