Present Perfect's explanations vs What it really is?

Question

First of all, I wish to say I'm kind of confused about the explanations for the present perfect and what really is the present perfect. I've came across many sites saying that the Present Perfect is:

Something that links the past to the present. (Eg. I have been to London - means that this somewhat affect the present for a reason)

(Which doesn't make any sense to me, since the sentence "I have left home" and "I left home" have the impact in the present - I'm not at home)

Something that happened at the past and we don't tell when. (Eg. I've liked you)

(Which is kind of strange IMHO, since I've came across these type of sentences: "I've been to Chicago (so far so good, didn't tell when). I went to visit him" (but I didn't tell when, so why is the past simple used?!))

Something that happened in the past and still goes on. (Eg . I have lived here for ten years)

(Agree with this one, although I know it's not this that the "Perfect* is about)

But I still don't get it. When I see the "Perfect" being used, I get confused why the "Simple" hasn't been used and vice-versa. And sometimes, I wonder what the meaning would be if either the "Perfect" or the "Simple" was used (since people tend to say "if you use 'x', means that you are focus on the action, whereas...")

So, could you please explain what really The Present Perfect is about? And how could I learn the sentences between the "Simple" and the "Perfect"? (I've trying to learn it for about 8 months smh)

*And I've also read the post that says about the Perfect tenses and how to use them, but that didn't make my questions disappear, unfortunately;

I thank you in advance.

Answer 1

See this post for am explanation of the usages of perfect - continuative, resultative and existential.

I have left home
I left home

I have left home is a continuative perfect- it implies some consequence that lasts to the present- for example, I walked out of the house, intending never to go back.

You don't generally use past simple without specifying when it happened, either explicitly or implicitly. There are exceptions, but in this case you would say something like:

I left home at 7:15 this morning
I left home when I was 17
Q: What did you do next? A: I left home.

The first does not imply a continuative effect, so we assume that you intend to return to your home, maybe later today. The second would mean that you left your parent's home when you were 17. We assume that the leaving home doesn't have a continuative effect because you now have a new home. The third, the when is implied by the context- the preceding question. The listener would know when next was, and the other circumstances surrounding the leaving.

I've been to Chicago
I went to visit him

I've been to Chicago is existential - we are talking about something that happened at an unspecified time in the past.

As mentioned earlier, you don't generally use simple past without a time.

I went to visit him yesterday
Q What did you do about that? A: I went to visit him

If you really don't want to say when you went, you would use an existential present perfect:

I have been to visit him