Sometimes the past simple and the present perfect are confused. It is important to remember that the past simple is used to express a finished past action which occurs at a specific moment in the past. The present perfect is used to express something that happened at an unspecified moment in the past. For example, if I visited Paris in 2004, I could express this in two ways:
I visited Paris in 2004.
I went to Paris a few years ago.
Note that the moment in time is specific - in 2004, a few years ago.
I've been to Paris.
I've visited Paris.
In this case, the moment of my visit is not specific. I am speaking about an experience that I have had in my life up to this moment in time.
This is the key to understanding the difference between the past simple and the present perfect. The past simple expresses something which happened at a specific time in the past. The present perfect expresses something that I have experienced in my life without giving the exact time.