one of the easiest things about learning English is how relatively few tenses there are (e.g. no future or conditional as such)
Sorry, but are we talking about the same 'English' here?! Our perception, and hence verbalization, of time is one of the most difficult things for foreign learners, and especially for Poles ... we have (arguably):
present simple / continuous
past simple / continuous
present perfect simple / continuous
past perfect simple / continuous
five ways of referring to future time (future with 'will', present simple for timetables, present continuous for arrangements, 'going to' for plans)
future perfect simple/continuous
genuine conditionals (would, etc.)
and all the above also active and passive ...
? How is that easy, and in what way do we have relatively few tenses? We have more tenses that a lot of languages, and make distinctions of time/perspective that other languages don't (which is the difficulty in explaining/learning).
Ok ... sorry ... small rant over ... but just don't want you to think our tense system is 'easy', as it is (notoriously) not so.
As for how to explain the present perfect ; ) ... think of the actual words you use.
I have been.
ie, I possess that action. It is mine. I present it to you. The significance of it is that I own it - I have experienced it. And I am still here, holding it, showing it to you.
Try to feel what it really means. Then it will be easier to communicate.