Present Perfect
1. д\выражения действия, которое уже завершилось и к моменту речи мы имеем результат в настоящем
She has cooked dinner. We can go for a walk.
Указатели:

just
never
ever
already
yet (-,?)
always
recently
lately
so far
today
this week (day,..)
before

She has already done her homework.
2. с предлогами
for (2 days, ages,…)
since (August, last year,…)
I have had a dog for 2 years.
3. с союзом  since в сложном предложении
Pr. Perfect      since           Past Simple
They have been good friends since they met in Paris.
4. в специальных вопросах How long…?
How long have you been married?
но How long ago did you understand it? – Past Simple
5. После It’s the first \second\.... time
It’s the first time I have been on a plane.