Present perfect

Present perfect:

We use the present perfect tense when we want to talk about:

- An event which started in the past, continuous, in the present and may continue in the future. 

Example

My parents have been married fot forty years.

- A recent event in the past which has relevance to the present. 

Example

A man has appeared in the court changed with the number of the missing person.

-An event which happened In the past without saying when it happened because we do not consider this is important.

Example

I have read Hamlet, but I have never seen it performed.

Have you seen John? 

- An event which happened in the past, but in unfinished time ( with expressions like today- this month- this year etc)

Example

I didn't see him last week, but I have been out with him twice already this week.