1. to talk about actions that happened in the past and we don't say when these actions happened.
The exact time is not mentioned because it is not important or not known.
They have bought a new car.
(When did they buy their car? It is not important. What is important is the fact that they have got a new car.)
2. to talk about actions that have recently finished and their results are visible in the present.
Harry has broken a cup.
(We can see a broken cup on the floor.)
3. to talk about actions that started in the past and are still continuing in the present.
Ann has been a doctor since 2015.
(Ann started working as a doctor in 2015 and she is still a doctor.)
4. with superlative adjectives
That’s the best film I’ve ever seen.
5. "have gone to / have been to"
They have gone to London.
(This means that they are still in London. They haven't come back yet.)
They have been to London.
(This means that they have visited London. But they are not there now. They have come back.) 
6. with time expressions (e.g. today, this morning, this week, etc.) when these periods of time are not finished at the time of speaking.
I have made several phone calls this morning.             
(It is still morning.)

I made several phone calls this morning.                
(It is evening now.)