And where is the question?
Maybe you just want to know about this tense in particular and when to use it ?
The Present Perfect Tense is used to describe actions that started in the near past and are either continuous in the present or JUST terminated at the present time.
Those are exactly the cases when you use that tense :
* There is a connection with the past.
He has just finished his meal.
* The exact time of the action is not known.
We have not known him for very long.
* "For" and "since" can be used to state the time of the action.
- I have learned English since 4 years.
* The action is not completed at the time of speaking/writing.
- She has just sent them the email.
* The action has been repeated numerous time, and is expected to be repeated in the future.
- I have seen him several times in different occasions.
The tense is formed by using the auxiliary verb 'have' and the participle of any verb as in :
have + done