The simple answer is that the Present Perfect is a look at the past from the point of view of the present. It can only express that something has happened, not exactly when it happened. The Past Simple expresses the point of view of the past directly and can express exactly when something happened.

The Present is an anchor tense for the Present Perfect ("have/has") and the Future of the Present ("will"). In parallel, the Past is an anchor tense for the Past Perfect ("had") and the Future of the Past ("would").

I have seen "Gone With the Wind". This is a claim that I have seen the movie. Nothing is said about when.

I saw "Gone With the Wind" ten years ago. This adds the "when" information.

There is much, much more to it than this brief post. Use Google or some other search engine to look for "Past Simple" and "Present Perfect". You will find loads of useful information.

Good luck on your adventure with English!