I am getting mix signals from different sources regarding Present Perfect (PP) and Present Perfect Continuous (PPC).
'When the acction occured' can not be used with PP at all, only with PPC.
The base form for PP is "I have done my homework" and for PPC is "I have been doing my homework for 2 hours."
So far so good, got it.
However, I am also seeing in numerous examples this two types of sentences.

Example A)
(PP) I have studied English for 3 years.
(PPC) I have been studying English for 3 years.

Or

Example B)
(PP) I have studied English since 2011.
(PPC) I have been studying English since 2011.

Are they both correct, and this tenses are interchangable in the "for" and "since" form?
Or to be on the safe side, should I stick with PPC as an only correct form in both examples?

Thank you!
Binka nljubinka@hotmail.com

PP refers to an action that is complete at the time of speaking.
PPC refers to an action that has started in the past and is still in progress.

(PP) I have studied English for 3 years.
- Because you are continuing to study, no action has been completed. You cannot use PP.

If you changed it to: Until this point, I have studied English for 3 years. Then the PP form can be applied because you are completing the action and it's no longer continuous.

(PPC) I have been studying English for 3 years.
- For this example it states that you have started studying 3 years ago and are continuing to study. Your action has started in the past and keeps going.

(PP) I have studied English since 2011.
- Because no action has been completed you cannot use PP.

(PPC) I have been studying English since 2011.
- For this example it states that you started studying in 2011 and are continuing to study.

I'll give a couple more examples that are mistakes and less ambiguous so it's easier to understand.

Mistake 1:
(PP) I have waited for half an hour.
- Because you are still waiting and the action has not been completed this is not correct.

Correct Version:
(PPC) I have been waiting for half an hour.

Mistake 2:
(PPC) He has been writing many books.
- Because you have specified the amount of completed books the action is not continuous and you cannot use PPC.

Correct Version:
(PP) He has written many books.

WOW!
Thank you so much, that was a fab answer. Got it :)

I can not understand passive voice properly?What should I do?

Not really sure why you posted in here but http://www.grammar-monster.com/glossary/passive_voice.htm explains pretty much everything you need to know.

Basically passive voice is when the subject of the sentence isn't doing anything, it's passive. It's not acting, it's being acted upon. I'll grab a couple examples from that link and explain why they are what they are.

Examples:

(Passive) The crowbar was used to open the window.
- What is this sentence about? It's about the window. What happened to the window? It was opened by the crowbar. So the window is the subject, but it does nothing, it merely exists.

(Active) The burglar used a crowbar to open the window.
- What is this sentence about? It's about the burglar. The subject isn't the window anymore. What is the burglar doing? Using a crowbar. This is active voice because the subject of the sentence is doing some sort of action.

(Passive) The tin of tuna fish was opened by Sasha.
- What is this sentence about? It's about the tin of tuna fish. What happened to the tin of tuna fish? It was opened by Sasha.

(Active) Sasha opened the tin of tuna fish.
- What is this sentence about? It's about Sasha. What did Sasha do? Opened the tin of tuna fish.

So how do you spot passive and active voice? It's all about what is going on in the sentence. Is something acting or is something being acted upon? If you look at the passive examples you'll see very clearly that something is happening TO something. If you look at the active examples you'll see that something is DOING something. That is the key, focus on that and the rest is clear.