[chryuop]

The fact is that the same difference you have it in English. He went to the library and he has gone to the library.
Unfortunately "have done" form in English has a wider ranger of meanings and some of them is not represented with -teiru. For example the present perfect can be used to give an idea of an experience had sometime in the past (have been to Japan, have gone to that restaurant before...) and in this case in Japanese you will use another way of saying the same thing.
In the same way the -teiru form is used to express ideas that the present perfect won't. For example you can use the -teiru form to give an idea of an action done more times as a habit, thing that you would show in English with the simple present.

That is why many people give you different answers to your questions. They can mean the same thing, but they cannot.