ARTICLE

ARTICLE 

Definition: English has two types of articles: definite (the) and indefinite (a, an.) The use 
of these articles depends mainly on whether you are referring to any member 
of a group, or to a specific member of a group:
Indefinite articles - a and an (determiners)

A and an are the indefinite articles. They refer to something not specifically known 
to the person you are communicating with.

A and an are used before nouns that introduce something or someone you have not 
mentioned before:
 My Opinion Examples:

• In the circuit an umbrella girls is important thing
• There is a man who talk too much

You use a when the noun you are referring to begins with a consonant 
(b, c, d, f, g, h, j, k, l, m, n, p, q, r, s, t, v, w, x, y or z), for example, "a city" and "a factory

You use an when the noun you are referring to begins with a vowel (a, e, i, o, u)

Pronunciation changes this rule:

If the next word begins with a consonant sound when we say it, for example, 
"university" then we use a. If the next word begins with a vowel sound when 
we say it, for example "hour" then we use an.

Examples:

• We say "university" with a "y" sound at the beginning as though it were spelt "youniversity".
  So, "a university" is correct.
• We say "hour" with a silent h as though it were spelt "our".
  So, "an hour" is correct.

Definite Article - the (determiners)

You use the when you know that the listener knows or can work out what particular person/thing you are talking about.
Example:

• The dog (that specific dog)
• The apple (that specific apple)

You should also use the when you have already mentioned the thing you are talking about.

My Opinion Example:

• there is a lot of the page i've been read

We use the to talk about geographical points on the globe.

Example:

• the Middle East, the West

We use the to talk about rivers, oceans and seas

Example:

• the Nile, the Pacific

We also use the before certain nouns when we know there is only one of a particular thing.

Example:

• the rain, the sun, the wind

However if you want to describe a particular instance of these you should use a/an.

Example:

• "I could hear the wind." / "There's a cold wind blowing."

1. indefinite article: a and an

1. We use the indefinite article, a/an, with count nouns when the hearer/reader does not know exactly which one we are referring to:

Police are searching for a 14 year-old girl.

2. We also use it to show the person or thing is one of a group:

She is a pupil at London Road School.

Police have been searching for a 14 year-old girl who has been missing since Friday. Jenny Brown, a pupil at London Road School, is described as 1.6 metres tall with short blonde hair. She was last seen wearing a blue jacket, a blue and white blouse and dark blue jeans and blue shoes. Anyone who has information should contact the local police on 0800349781.

3. We do not use an indefinite article with plural nouns and uncount nouns:

She was wearing blue shoes. (= plural noun)
She has short blonde hair. (= uncount noun)

Police have been searching for a 14 year-old girl who has been missing since Friday. Jenny Brown, a pupil at London Road School, is described as 1.6 metres tall with short blonde hair. She was last seen wearing a blue jacket, a blue and white blouse and dark blue jeans and blue shoes. Anyone who has information should contact the local police on 0800349781.

4. We use a/an to say what someone is or what job they do:

My brother is a doctor.
George is a student.

5. We use a/an with a singular noun to say something about all things of that kind:

A man needs friends. (= All men need friends)
A dog likes to eat meat. (= All dogs like to eat meat)

2.definite article: the

The definite article the is the most frequent word in English.
We use the definite article in front of a noun when we believe the hearer/reader knows exactly what we are referring to.
• because there is only one:

The Pope is visiting Russia.
The moon is very bright tonight.
The Shah of Iran was deposed in 1979.

This is why we use the definite article with a superlative adjective:

He is the tallest boy in the class.
It is the oldest building in the town.

• because there is only one in that place or in those surroundings:

We live in a small village next to the church.	=	(the church in our village)
Dad, can I borrow the car?	=	(the car that belongs to our family)
When we stayed at my grandmother’s house we went to the beach every day.	=	(the beach near my grandmother’s house)
Look at the boy in the blue shirt over there.	=	(the boy I am pointing at)

• because we have already mentioned it:

A woman who fell 10 metres from High Peak was lifted to safety by a helicopter. The woman fell while climbing.
The rescue is the latest in a series of incidents on High Peak. In January last year two men walking on the peak were killed in a fall. 

We also use the definite article:

• to say something about all the things referred to by a noun:

The wolf is not really a dangerous animal (= Wolves are not really dangerous animals)
The kangaroo is found only in Australia (= Kangaroos are found only in Australia)
The heart pumps blood around the body. (= Hearts pump blood around bodies)

We use the definite article in this way to talk about musical instruments:

Joe plays the piano really well.(= George can play any piano)
She is learning the guitar.(= She is learning to play any guitar)

• to refer to a system or service:

How long does it take on the train.
I heard it on the radio.
You should tell the police.

• With adjectives like rich, poor, elderly, unemployed to talk about groups of people:

Life can be very hard for the poor.
I think the rich should pay more taxes.
She works for a group to help the disabled.

The definite article with names:

We do not normally use the definite article with names:

William Shakespeare wrote Hamlet.
Paris is the capital of France.
Iran is in Asia.

But we do use the definite article with:

• countries whose names include words like kingdom, states or republic:

the United Kingdom; the kingdom of Nepal; the United States; the People’s Republic of China.

• countries which have plural nouns as their names:

the Netherlands; the Philippines

• geographical features, such as mountain ranges, groups of islands, rivers, seas, oceans and canals:

the Himalayas; the Canaries; the Atlantic; the Atlantic Ocean; the Amazon; the Panama Canal.

• newspapers:

The Times; The Washington Post

• well known buildings or works of art:

the Empire State Building; the Taj Mahal; the Mona Lisa; the Sunflowers

• organisations:

the United Nations; the Seamen’s Union

• hotels, pubs and restaurants*:

the Ritz; the Ritz Hotel; the King’s Head; the Déjà Vu

*Note: We do not use the definite article if the name of the hotel or restaurant is the name of the owner, e.g.,Brown’s; Brown’s Hotel; Morel’s; Morel’s Restaurant, etc.

• families:

the Obamas; the Jacksons

Source : http://aderikardo.blogspot.com/2012/09/determiner-quantifier.html