This difference is taught at the end of elementary level - if you want to be above elementary level in English, you really can't ignore it! :)
The good news is that this is a common question from learners, and there are already just as many answers. There are also plenty of exercises online:
The very simple difference between the two grammar forms is this: present perfect always describes the present situation. Simple past only describes the past (and you need to tell us when the event happened).
So, are you talking about the situation at this moment, or are you telling a story from the past?