THE PRESENT PERFECT
1. The Form:
It is formed with two elements :
-Have / Has (present tense), + the past participle
(The PP of Regular verb is verb+ed, For example: played, arrived, looked.)
(The PP of Irregular verbs, Lokk at p. 155/157 of your books for the list of irregular verbs
I have seen "the Titanic" several times.
I have never seen that movie.
NOTE: When you are using adverbs (already, never, just) they usually come between the first part and the second part (have never seen).
2. The use:
The Present Perfect is used to show a relation between the present and the past. The time of the action is before now but it is not specifically mentioned and we are intrested in the result more than in the action.
The present perfect describes :
1. An action or situation that started in the past and continues in the present:
Ex: I have lived in Tetuan since 1997 (= and I still do.)
2. An action that started in a time that has not yet finished:
Ex: She has been to the cinema twice this week (= and the week isn't over yet.)
3. A repeated action in an unspecified period between the past and now:
Ex: We have visited Agadir several times.
4. An action that was completed very recenttly usingthe adverb 'just').
Ex: I have just finished reading Taha Hussein's "Al-Ayyam".
5. An action when the time is not specified because it is not important.
Ex: He has watched the match between Tangier and Tetuan. (the fact of watching the match is more important than the time of watching it)
We use the SIMPLE PAST when we want to ask more specific information about when,where, who ...
Ex: He watched the match last Sunday.