Present perfect

Present Perfect
FORM
[has/have + past participle]
Examples:
* You have seen that movie many times. * Have you seen that movie many times? * You have not seen that movie many times.
Complete List of Present Perfect Forms
USE 1 Unspecified Time Before Now

We use the Present Perfect to say that an action happened at an unspecified time before now. The exact time is not important. You CANNOT use the Present Perfect with specific time expressions such as: yesterday, one year ago, last week, when I was a child, when I lived in Japan, at that moment, that day, one day, etc. We CAN use the Present Perfect with unspecific expressions such as: ever, never, once, many times, several times, before, so far, already, yet, etc.
Examples:
* I have seen that movie twenty times. * I think I have met him once before. * There have been many earthquakes in California. * People have traveled to the Moon. * People have not traveled to Mars. * Have you read the book yet? * Nobody has ever climbed that mountain. * A: Has there ever been a war in the United States?
B: Yes, there has been a war in the United States.
How Do You Actually Use the Present Perfect?
The concept of "unspecified time" can be very confusing to English learners. It is best to associate Present Perfect with the following topics:

TOPIC 1 Experience
You can use the Present Perfect to describe your experience. It is like saying, "I have the experience of..." You can also use this tense to say that you have never had a certain experience. The Present Perfect is NOT used to describe a specific event.
Examples:
* I have been to France.
This sentence means that you have had the experience of being in France. Maybe you have been there once, or several times. * I have been to France three times.
You can add the number of times at the end of the sentence. * I have never been to France.
This sentence means that you have not had the experience of going to