We use the Present Perfect Simple to talk about actions that:
a started in the past and are still happening.
How long have human being lived on Earth?
b have just finished.
l've just found a really good websit about astronomy.
c happened in the past but we don't say exactly when.
He's met the famous astronaut,Neil Armstrong.
d happened in the past but have a result that affects the present.
lngrid has washed her hair and it's still wet.