Denifinte and Indefinite Articles

What is a definite article? A definite article is a determiner that restricts or particularises a noun. In English there is only one definite article that is 'the'. 'The' is mostly used when we refer to a thing which is only one and nothing more but one! The examples for the usage of the definite article in this case are: "the sun" (we have only one sun..... you can't find another sun elsewhere in your life!), "the moon", "the earth", etc...

A definite article is also used when we refer to a thing that has already been mentioned before! The following example will explain the usage:
"There is a book on the table"
"Can you give me the book, please?"

A definite article is also used to show the superlative degree of an adjective. Check the following examples:
"They three are smart students but Arif is the smartest amongst the three"
"Amongst the countries in ASEAN, Indonesia is the biggest country by area and by population".

Now, what is an indefinite article? An indefinite article is a determiner that expresses nonspecificity of a noun. There are a lot indefinite articles in English that are "a", "an", and "some" to say three of them. "a" and "an" are used for singular nouns whilst "some" are used for plural nouns. "a" is used for a noun that starts with consonant sounds while "an" is used for a noun that starts with vowel sounds.

The examples for the usage of "a" and "an" are:
"a balloon"
"a cat"
"a car"
"a piano"
"a computer"
"a university" etc...

"an apple"
"an orange"
"an orangutan"
"an umbrella"
"an hour" etc...

The example for the "some" usage is given below in sentences:
"I remember there are some apples in the fridge. If I'm not mistaken there are three of them!"
"There are some students in the class. Maybe there are about ten of them in it!"