The difference between Present Perfect and Simple Past is that the first is somehow connected to the present and the latter is not. However, it seems to me that "connected to the present' is a little subjective and that deciding whether an event is connected to the present depends on the speaker's interpretation of the context.
My latest question about the difference between both verb tenses is the verb "to come". What is the difference between "came" and "have come" ? Does the latter implies that the subject still is at the place? Or could it mean other connection to the Present, eg "He has come to the beach and has got a sunburn" (assuming that he is currently suffering the effects of the sunburn) ?
Furthermore, what is the correct verb tense in the sentence: "He has come to see if I am/was ok" ? I guess this is related to the above question.
Note: I'm aware that US English uses Simple Past in some contexts where UK English would use the Present Perfect, probably because it simplifies the whole process of deciding whether every event has a connection to the present or not when talking.