The 3 articles in English are a, an and the. 

The student needs to choose thing by-thing which one of the articles to utilize. 
The word a (which turns into a when the following word starts with a vowel - a, e, I, o, u) is known as the inconclusive article on the grounds that the thing it runs with is uncertain or general. 
The significance of the article an is like the main, however one is more grounded and gives more accentuation. 
It is conceivable to state I have a book or I have one book, yet the second sentence underscores that I don't have a few or some other number of books. 

 The word the is known as the positive article and demonstrates a particular thing. The contrast between the sentences I sat on a seat and I sat on the seat is that the second sentence alludes to a specific, particular seat, an extraordinary seat. 

 Numerous things, particularly solitary types of countable things must have an article. In English, it isn't conceivable to state I sat on the seat without an article, yet a decisive or possessive descriptive word can be utilized rather than an article as in the sentences I sat on that seat and I sat on his seat. 

Types of article

Articles with countable and uncountable nouns exercises
Articles with countable and uncountable nouns exercises

Indefinite Articles

'a or an' are indefinite articles and are used when to say about not a definite person, place or thing.
Example : 
I saw a girl. (any girl --not definite)
He gave me an orange.

Definite Articles

'the' is called a definite article and is used when to say about a definite person, place or thing.
Example : 
I saw the girl who secured the first rank. (girl --is definite)

Usage Of Definite Articles 'the' is used before the following common noun. 
Example: the sun, the moon, the planet, the sky, the earth
'the' is used before a particular person or thing already referred to. 
Example: The boy whom I met yesterday.
The book that I gave you.
'the' is used before some books. Example: The Ramayana, The Koran, The Bible.
'the' is used before the name of rivers, mountain, seas, oceans, islands..etc. Example: The Ganges, The Nile, The Laccadive.
'the' is used before a singular noun that represents the whole class. Example: The cows a domestic animal.
The rose smells sweet.
The parrots a beautiful bird.
'the' is used before superlatives. 
Example: The highest mountain in the world.
The best picture I have ever seen.
'the' is not used before a proper noun. 
Example : Mumbai is a major port in India.
Pacific is the deepest ocean.

You cannot say a/an with an uncount noun.

You can't put a number before an uncount thing. (You can't make an uncount thing plural.) 
You utilize an uncount thing with no article on the off chance that you imply that thing when all is said in done. 
You utilize the with an uncount thing when you are discussing a specific case of that thing. 

Count Noun

You can put a number before a Count Noun. (You can make the most of a thing plural.) 
You can put both a/an and the before a Count Noun. 
You should put an article** before a particular Count Noun. 
You utilize a plural tally thing with no article on the off chance that you mean all or any of that thing. 
You, as a rule, utilize an/a with a check thing the first occasion when you say or compose that thing. 
You utilize the with Count Nouns: 
the second and resulting times you utilize the thing in a bit of discourse or composing 
at the point when the audience recognizes what you are alluding to (possibly in light of the fact that there is just a single of that thing) 
You utilize a (not a) when the following word (intensifier, descriptor, thing) begins with a vowel sound. 

 Note 
The above standards apply whether there is or there isn't a modifier before the thing. 
A few things can be either Count or uncount, contingent upon the specific situation and significance: 
Do you have paper? I need to draw a photo. (uncount = a sheet of paper) 
Would you be able to get me a paper when you're at the shop? Count = a daily paper) 
Uncount things are frequently gone before by expressions, for example, a great deal of .. (good fortune), a bit of .. (cake), a jug of .. (drain), a grain of .. (rice). 
* Instead of an article, the thing can likewise be gone before by a determiner, for example, this, that, a few, numerous or my, his, our, and so on 

 Following are probably the most vital rules recorded above, with illustration sentences: 
You utilize an uncount thing with no article on the off chance that you mean all or any of that thing. I require help! 
 I don't eat cheddar. 
Do you like music? You utilize the with an uncount thingwhen you are discussing a specific case of that thing. Thanks for the assistance you gave me yesterday. I didn't eat the cheddar. It was green! 
Did you like the music they played at the move? 
You, for the most part, utilize an/a with a count noun the first occasion when you say or compose that noun. Can I obtain a pencil, it would be ideal if you There's a feline in the garden! 
Do you have an mp3 player? 

 You utilize the with count Noun  the second 
what're more, consequent occasions you utilize the thing, or on the other hand when the audience definitely recognizes what you are alluding to (possibly in light of the fact that there is just a single of that thing)? Where's the pencil I loaned you yesterday? 
I think the feline has a place with the new neighbors. 
I dropped the mp3 player and it broke. 
If you don't mind close the entryway! 
You utilize a plural check thing Count noun an article in the event that you mean all or any of that thing. 
I don't care for canines. 
Do they have kids? 
I needn't bother with questions. Give me answers!