The present perfect tense is always related to the present time. The action in the present perfect always has some kind of impact on the present moment. For example, if you say 'I have met him' it means that you are now acquainted with that person. If you say 'We have just finished cleaning up the desk', it could mean that the desk is now clean and tidy, or it could mean that you're tired from the exertion of cleaning up the desk, or it could mean that you are now free to take on another task. Whatever you mean, it always refers in some way to the present situation.

The past perfect tense (more precisely, the "past perfect time aspect"), can have different connotations depending on context, like in all languages. #1 does not necessarily imply a continuation up to the present. It might be used in the sense of "I have met him [before/previously], indicating that the action occurred in the past but implying connection between the present action (meeting him again) and the past action (having already met him). #2 does imply a continuation to the present. The phrase "just finished" tells us that the action was completed very, very recently. "Just" is a qualifier (similar to adjective/adverb), which tells us that the verb phrase "have...finished" continued up to the present moment.

Present perfect tense has many uses. One of them is to show "life experience". I've done that before. I've met him already. I've seen that movie before. I've been married before. (no relationship to the present)

Thanks for your detailed explanation.^^

Think of Item 1 by imagining adding the words, "... in my life" at the end. Then you will more clearly see the difference between "I have met him" and, e.g., "I met him in 2012." The second, past tense form tells when the meeting happened, while the first, present perfect tense form talks about the fact that you met him at some point in your life. It would be the same as saying, "I have visited Jeonju" (meaning in your life, whether it was once or ten times) vs. "I visited Jeonju in 1997" (referring to a specific completed trip).