Having it now doesn't necessarily lead only to the present perfect though. Consider the following exchange:
Have you found your sleeping bag?
Yes. I've found it.
Where did you find it?
I found it in the attic.
When did you find it?
I found it yesterday.
Although it appears that the person probably does still have their sleeping bag, having found it yesterday, that only leads to the present perfect being used in the first past of this exchange. For the other two exchanges, one which gives a location and one which gives a timing, the past simple is perfectly adequate.
However, in line (to a certain extent) with Boris' explanation involving the whereabouts of the item now, consider the following:
Have you found your sleeping bag?
Well, I found it but then I lost it again!
or
Well, I found it but now I've lost it again!
Advice for Batman 45 - we are happy to help where we can but as we say frequently, we are not here to replace dictionaries, grammar books/websites or your own study. Even though you came to English late, there is nothing to stop you studying it formally. I suggest you get a good grammar book with exercises and work through it in your own time. When you come across something that you still can't quite get your head around, feel free to ask us, giving details of what you've studied so far, what the exercise was and why you are confused.