present perfect (have verbed) is very common, but it is definitely the most confusing tense in English. The basic idea is "mixing past and present"--something isn't really in the past, and it isn't really in the present. This can happen a few different ways.
1. The fact can still change. It is true now, but if you ask me tomorrow, I might give a different answer.
She had 5 husbands= she is dead. The number cannot change.
She has had 5 husbands= She is still alive. She can divorce #5 and marry a sixth husband if she wants to.
I never went to that restaurant=the restaurant is permanently closed. I can't go there now.
I have never gone to that restaurant= I can go tomorrow if I decide to.
--You will often see present perfect used this way when you count things (5 husbands), or when you say "not" or "never"
--if you mention a time span that is OVER (yesterday, last year), you should use past simple (verbed). If you mention a time span that is CONTINUING (today, this year, my life), you should USUALLY use present perfect
I didn't eat lunch YESTERDAY.
I haven't eaten lunch TODAY.
I watched that movie 5 times yesterday.
I've watched that movie 5 times today.
2. You mention the past to explain the present.
I haven't eaten breakfast yet. Let's go eat something.
I've already eaten breakfast, so I'm full.
3. You make conclusions about the past based on evidence in the present.
Look! someone has left a wallet on the table!