present prefect vs pastperfect

What is the different of past perfect tense and present perfect tense???

(1)Past perfect, http://www.edufind.com/english/grammar/Tenses11.cfm The past perfect refers to a time earlier than before now. It is used to make it clear that one event happened before another in the past. It does not matter which event is mentioned first - the tense makes it clear which one happened first.e.g. I had saved my document before the computer crashed. He was very tiredbecause he hadn't slept well. (2)Present perfect, http://www.edufind.com/english/grammar/Tenses4.cfm
The 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 is used to describe:1.An action or situation that started in the past and continues in the present. Example: I have lived in Bristol since 1984 (= and I still do.)

2. An action performed during a period that has not yet finished. Example: 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. Example: We have visited Portugal several times.

4. An action that was completed in the very recent past, (expressed by 'just'). Example: I have just finished my work.

5. An action when the time is not important. Example: He has read 'War and Peace'. (the result of his reading is important)Note: When we want to give or ask details about when, where, who, we use the simple past. Example: He read 'War and Peace' last week.

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Present perfect is sth still related to 'now'.
eg: I have lived here for 10 years.
(I lived here before, but I am still living here)
Past Perfect is sth before the past.
eg: (I had taken John to the park, before you came back)
(John has already finish going to the park)
*** After using past perfect, usually the previous or the next sentence is using past tense!!!