present perfect -it describes an event whitch recently happened -an action whitch just ended -it is used to speak about an event whitch continues up to now (the action finished just now or continues) past simple - the action is ended in the past (no relation with the present)

Use the past simple to talk about finished events in the past. Use it to tell stories, jokes and anecdotes. The present perfect is used for several reasons: 1) Use it to describe events that happened in the past and are still true now because you can see the result. I’ve broken my leg! David has painted his house. 2) Use it to describe experiences in your life. I’ve been to New York three times in my life. However, you cannot use the present perfect to describe experiences in someone’s life if that person has died. Michael Jackson performed in Britain many times. NOT Michael Jackson has performed in Britain many times. 3) Use it to describe events that started in the past and are still happening now. I’ve lived here all my life (and I live here now). John has worked here for 10 years (and he works here now). Never refer to a finished time with a present perfect verb.

There's no short or easy answer. These sentences say basically the same thing: - I carried the box - I have/I've carried the box 1. To show emphasis in speaking, you'd stress "have" in the perfective. This means you *truly* or *really* carried the box (it was *not* someone else, or something else.) 2. You can almost always use the simple past in everyday speech, it is very natural: - I finished - I have finished (< requires saying an extra word! who has time for that?) 3. We use adverbs to help clarify the meaning (this is very common): - I carried the box today - I have often carried the box I'm sure you'll get more pedantic answers, this is as simple as I can make it.