We use the past perfect when we wish to stress that one action or situation in the past occurred before another action or situation in the past.
It was obvious that something had happened to them. (It had happened before it became obvious)
I had been waiting for more than an hour when they arrived. (When they arrived I had already been waiting …)

The past perfect can serve the same purpose as conjunctions of time such as when, after and before:
When she (had) finished her work she left the office.
After Jimmy (had) arrived, the party became really good.
Before he retired my father (had) worked in the post office.

Notice that it is not normally necessary to use the past perfect in these situations, but it is quite common to do so, especially with the conjunction when, which has several different meanings and may need to be clarified.

By using a combination of these conjunctions and different tenses we can not only explain ourselves more precisely, but also be less repetitive.

As with most verb tenses, the past perfect has both a simple and a continuous form:
I had talked to all of the candidates by lunchtime.
I had been talking so much that I was starting to go hoarse.

While the simple form is used to stress the fact that the action was finished (i.e. there were no more candidates to talk to), the continuous form stresses the continuation of the activity (i.e. I would (probably) talk some more).

Another difference is that we tend to use the past perfect simple to speak about situations that lasted a long time, or were permanent, while the past perfect continuous is for more temporary or short-term situations or actions:
By that time the Moors had lived in southern Spain for over 700 years.
I had only been living in London for a week when I found a job.

There are also some verbs (called stative verbs) that are not usually used in the continuous form, even though that tense would seem to be more appropriate.

We also use the past perfect tense with verbs like want, plan, intend, hope, etc. to speak about things that we planned to do but could not for some reason:
We had wanted to see Susie run, but got caught up in the traffic.
I had planned to read the report but just didn’t have time.

Finally, the past perfect tense is also used in third conditional sentences.

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We use the past continuous tense to say that something was happening around a particular time in the past. The action or state began before this particular time, but had not yet finished:
I was watching television at 9 o’clock last night. (I started watching TV before 9 o’clock and I finished after 9 o’clock).

We often use the past continuous tense and the past simple tense together. The past continuous is used to “set the scene”, or provide (longer) background information. The past simple is used to speak about shorter actions that happened in the middle of the longer action, or that interrupted it:
The young couple were walking home together after the party. They were holding hands and were speaking excitedly about their plans. Suddenly, something moved in the shadows …
I was watching television when the neighbours came to visit.

We tend to use the past continuous tense to speak about more temporary situations and actions, while we use the past simple to refer to more permanent ones:
I was working in that bookshop for a few days last summer.
She worked in the bookshop for 41 years.

Note that there are some verbs (called stative verbs) that are not usually used in the continuous.

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The passive is formed with the verb to be (is/was/have been etc.) and the past participle (done/cleaned/seen etc.):
The sculpture is made of glass and plastic.
That toy was made in China.
All staff have been informed of the changes.

The following forms are common:

http://www.edufind.com/english/grammar/Pass1.cfm

When we say what a person or thing does, we use an active verb:
My brother built his own house.
We all speak Spanish.
The man is repairing the fridge at the moment.

When we say what happens to a person or thing – what is done to them – we use a passive verb:
All of those houses were built by my brother.
Spanish is spoken in most Latin American countries.
I came by bus because my car is being repaired.

Some verbs cannot have passive forms. Intransitive verbs , such as sleep, die, fall, or arrive, which do not take an object, do not have a passive form.

Also, stative verbs are not usually used in the passive.
We all have university degrees (NOT University degrees are had by us all)
I see what you mean (NOT What you mean is seen by me)

Many learners confuse active and passive verb forms because, as Swan points out in Practical English Usage (OUP; 1997) :

“Be is used to make both passive verb forms and active progressive tenses.”

p. 409
Your orders are being processed right now.
We are processing your orders right now.

And “past participles are used to make both passive verb forms and active perfect tenses.”

p. 409
The toy was made in China.
He has made a terrible mistake.

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A part of speech (also word class) is any of the grammatical groups into which words are divided depending on their use.

The following are the different parts of speech in English grammar:

Adjective
A word that describes a noun or pronoun. ‘
‘Big’, ‘boring’, ‘purple’, ‘quick’, ‘obvious’ and ’silvery’ are all adjectives.

Adverb
A word which describes or gives more information about a verb, adjective, adverb or phrase.

In the following sentences, ‘cheerfully’, ’spotlessly’, ‘extremely’, ‘well’, and ‘right’ are adverbs:
She smiled cheerfully.
The house was spotlessly clean.
He’s managing extremely well.
The shot was heard right outside the door.

Conjunction
A word such as ‘and’, ‘but’, ‘while’ or ‘although’ that connects words, phrases and clauses in a sentence.

Determiner
A word which is used before a noun to show which particular example of the noun you are referring to.
In the phrases ‘my first boyfriend’ and ‘that strange woman’, the words ‘my’ and ‘that’ are determiners.

Interjection
An interjection is a word which is used to show a short sudden expression of emotion.
“Hey!” is an interjection.

Noun
A word that refers to a person, place, thing, event, substance or quality.
‘Doctor’, ‘tree’, ‘party’, ‘coal’ and ‘beauty’ are all nouns.

A noun phrase is a group of words in a sentence which together behave as a noun.
In the sentences ‘We took the night train’ and ‘Do you know the man sitting in the corner’, ‘the night train’ and ‘the man sitting in the corner’ are noun phrases.

Preposition
A word which is used before a noun, a noun phrase or a pronoun, connecting it to another word.
In the sentences, ‘We jumped in the lake’, ‘There were cheers at the end of the performance’ and ‘She drove slowly down the track’, ‘in’, ‘at’, ‘of’ and ‘down’ are prepositions.

Pronoun
A word which is used instead of a noun or a noun phrase.

Pronouns are often used to refer to a noun that has already been mentioned.
‘She’, ‘it’ and ‘who’ are all examples of pronouns.

Verb
A word or phrase that describes an action, condition or experience.
The words ‘run’, ‘keep’ and ‘feel’ are all verbs.

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In his excellent Practical English Usage (Oxford University Press, 1997), Michael Swan explains the use of participles:

“a – verb forms

Participles are used with the auxiliary verbs be and have to make progressive, perfect and passive verb forms:
It was raining when I got home.
I’ve forgotten your name.
You’ll be told as soon as possible.

b – adjectives

Participles can be used like adjectives:
I love the noise of falling rain.
She says she’s got a broken heart.
John has become very boring.
The house looked abandoned.

c – adverbs

Sometimes participles are used like adverbs:
She ran screaming out of the room.

d – clauses

Participles can combine with other words into clause-like structures:
Who’s the fat man sitting in the corner?
Having lost all my money, I went home.
Most of the people invited to the party didn’t turn up.
Rejected by all his friends, he decided to become a monk.”

p. 401

Swan also points out that the names “present participle” and “past participle” are not very suitable, because both forms can be used to talk about the past, present and future:
“She was crying when I saw her.
Who’s the man talking to Elizabeth?
This time tomorrow I’ll be lying on the beach.
It was broken in the storm.
You’re fired.
The new school is going to be opened next week.”

p. 401

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