Present Perfect

Употребляется
Present perfect is used at the description of the event which took place in the past and being actual, essential, significant at the time of the speech about it.
Thus doesn't matter when this action happened.
Present perfect is used when action was already made, but time period when it occurred, didn't expire yet.

Схема
I
You
We
They
He
She
It
Have V3
has V3

The boy is reading a book.
The boy has read
the book.

Key words
already
just
ever
never
yet

Вопросы
We have already had dinner.
General:
We have already had dinner.
Tag question:
We have already had dinner, haven’t we?

Alternative question:
Have we already had dinner
or lunch?
Special question:
Who has already had dinner?
What have we already had?