Present Perfect

Use the present perfect for:

1. Life experiences in the past. We don’t say when these happened: we are interested in the experience, not the time or date. We often use ever and never.
   
   I’ve seen all Tarantino’s films.
   Have you ever eaten sushi? - Yes, I have. / No, I haven’t.
   
   
2. Recent past actions that are important now.
   
   Oh no! I’ve left my wallet on the bus.
   The president has resigned.
   
   
3. Past situations that are still happening now. We often use how long with for (throughout a period of time) and since (from a point in the past until now).
   
   I haven’t seen Jenny this morning. (It is still this morning.)
   How long have you known Mitya? - I’ve known him for two years.
   Jack's been in Italy since January.
   
   
4. With just, already, yet to talk about recent events in the past. The exact time is not important. Use just and already mainly in positive sentences. Use yet in negatives and questions.
   
   It’s just stopped raining. Let’s go out.
   Can you feed the cat? - I’ve already fed her.
   We can still watch the film. It hasn’t started yet.
   Have you done your English homework yet?

Note: Use the past simple for completed actions in the past.

I saw Jenny yesterday.
Peter moved to Saudi Arabia in 2011.
Natasha didn't want another piece of cake.
When did you see Alex?

Form:

For positive sentences:  subject + have/has + past participle.
For negative sentences:  subject + have/has + not + past participle 
For questions: have/has + subject + past participle?

I've finished the report.
Jack's been in Italy since January.
We've just got back from Germany.
I haven’t seen Jenny this morning.
How long has Alex known Mitya?