Present perfect

Use: I use the present perfect: the action was in past and its result is in the present.
Or: the action constantly was in past and it takes to present. The duration constantly to present.

Ex:
Have you heard from Thi recently?
I've met a lot of people in the last few dáy.
Everything is going well. We haven't had any problems so far.
I'm hungry. I haven't eaten anything since breakfast.
It's nice to see you again. We haven't seen each other for a long time.
It's the first good meal  
It's the first time something has happened