When do you use a Present Perfect?
* events which started in the past but the effect is still noticeable in the present (unfinished action/state, result)
* experiences in the past (date is not important)
Examples:
I have known Sally for 10 years. (You still know her now)
I can't run, I have broken my leg. (Your leg is still broken at this moment)
I have been to London six times. (Date is not important, you might go again)