Present Perfect is used to indicate a link between the present and the past. The time of the action is before now but not specified, and we are often more interested in the result than in the action itself.
The present perfect of any verb is composed of two elements. There are appropriate form of the auxiliary verb to have (present tense) and the past participle of the main verb. For examples :
a. She has visited
b. I have never seen snow.
c. Have you ever visited New York?
Noticed in the examples : the adverbs ever, never, already, yet, still and just are frequently used with the present perfect.
BE CAREFUL! There maybe a verb tenses in your language with a similar form, but the meaning is probably NOT the same.
The Present Perfect is used to describe :
1. A situation that started in the past and continues in the present. Example : I have lived in Seoul since 1995.
2. An action performed during a period that has not yet finished. Example : She has been to the cinema twice this week.
3. An action that was completed in the very recent past, expressed by just. Example : I have just finished my work.
4. An action when the time is not importan. Example : He has read newspaper.
5. An repeated action in an unspecified period between the past and now. Example : We have visited Spanyol several times.
NOTE : When we want to give or ask details about when, where, who. we use the simple past.
The present perfect when used with FOR and SINCE. Example :
a. I have been here since ten o'clock.
b. I have been known him for many years.
The difference between since and for :
a. Since + a particular time
b. For + a duration of time