Need clarification: Past perfect is used to indicated the sequence of past events

[H20]

hi everyone,

tense shifting has never been a problem for me in the past 8 years, but recently, I have been deeply troubled by perfect tenses. I've been reading rules and exampls of perfect tenses for a few months now, but I still feel very confused, even more confused than I first started. Now I'm hesihant to write or speak in English not because I'm scared of making mistakes, but because inundated by all the information, I don't know how to formulate my sentences anymore. I feel so many tenses are interchangeable, but somehow I know they are not. I don't really know how to explain all my confusion, I'll just write a few questions and see if you guys can help me with them.

1. Past perfect is used to indicated the sequence of past events; does present perfect do the same thing? Also, are there clear rules as to when to use each one? In many cases, I feel they both work.
ex1-> I have been to France before vs. I had been to France before.
ex2-> Nora wants to show her friends the pictures she took / has taken / had taken last summer

2. What's the difference between the following sentences:

- school has been cancelled
- school is cancelled

above sentences are both written in passive mode, are there rules for when to use which?

3. what's the difference between the following sentences:

- she was eating an apple.
- she had been eating an apple
- she has been eating an apple

4. which one of the following sentences is right or does it depend on situation or else they are all wrong:

-she might have been the nicest person I have ever met.
-she might have been the nicest person I had ever met.
-she might have been the nicest person I ever met.
-she might have been teh nicest person I met.

I thank you in advance for your help!!!!!!!!!!!!!

[Daemon99]

Here is my understanding of the perfect tenses. It could be wrong though. Please correct me if I am wrong.

When the point of reference in time is now (present), then you go for Present Perfect tense. If it's some time in the past, you go for Past Perfect.

For example, you went to France in 2006. You are talking to your friend now (2008).

You would say, "I have been to France before"

Now imagine you are narrating a story about something that happened in the past to your friend.

And the narration goes like this,

"It was in 2005 when I had this interesting conversation with a French guy.
We didn't understand each other as he couldn't understand English, and as you know, I don't speak French. I didn't know that the French weren't all that good at English. How would I know, I had never been to France before."

(here we are talking about 2005, and you did not ever visit France before that)

Here, you wouldn't say, "I have never been to France before", because you went there in 2006.
_________________
Non-native speaker of English
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I intend to live forever - so far, so good.

[H20]

Thank you daemon99!! I found a book in the library that totally clears all my inexplicable confusion. It's called Tense in English, and it's written by Renaat Declerck. I think it's for linguists since it's full of technical terms, but it's wonderful!!