Il Present Perfect Tense si forma con il verbo avere al presente + il participio passato del verbo. Il Participio passato (Past Participle) di un verbo regolare è identico al Simple Past e termina quindi con -ed.

I verbi irregolari hanno invece una loro forma particolare di participio passato.

il Present Perfect Tense

I have walked
You have walked
He has walked
She has walked
It has walked
We have walked
You have walked
They have walked

o, nella forma contratta...

I've walked
You've walked
He's walked
She's walked
It's walked
We've walked
You've walked
They've walked

Uso del Present Perfect

Il Present Perfect si usa per:

• Azioni iniziate nel passato e che continuano ancora... come ad esempio "Vivo a Firenze da 2 anni"... si accompagna quindi spesso a since, for...
  I have lived in Florence for two years. (significa che ci vivo ancora oggi...)
  I've worked here since 2004. (e ci lavoro ancora oggi...)
• Analogamente si usa quando il periodo di tempo di cui si parla è iniziato ma non ancora terminato.
  I've worked too much this week (la settimana non è ancora finita)
• Azioni avvenute nel passato in un periodo imprecisato
  Si accompagna quindi a... already, yet, ever, never... poste prima del participio passato.
  I've already seen that movie.
  Have you ever been in love?
  Have you ever been in Paris?
  Have you ever been in psychotherapy, Doctor?
  I've never been here before.
  
  The truth is I've never fooled anyone. I've let people fool themselves.
  Marilyn Monroe
  
• Azioni che, accadute in passato, continuano ad avere effetto sul presente...
  I've lost my keys. (non le ho ancora trovate)
  I've lost my mind (ho perso la testa... e anche ora non mi sono ancora ripreso)

I've learned that no matter what happens, or how bad it
seems today, life does go on, and it will be better tomorrow. I've learned that
you can tell a lot about a person by the way he/she handles these three things:
a rainy day, lost luggage, and tangled Christmas tree lights. I've learned that
regardless of your relationship with your parents, you'll miss them when they're
gone from your life. I've learned that making a living is not the same thing as
making a life. I've learned that life sometimes gives you a second chance.
I've learned that you shouldn't go through life with a catcher's mitt on both
hands; you need to be able to throw some things back. I've learned that whenever
I decide something with an open heart, I usually make the right decision. I've
learned that even when I have pains, I don't have to be one. I've learned that
every day you should reach out and touch someone. People love a warm hug, or
just a friendly pat on the back. I've learned that I still have a lot to learn.
I've learned that people will forget what you said, people will forget what you
did, but people will never forget how you made them feel.
Maya Angelou