Indefinite articles (a / an) are used before a noun to show that it is not specific, or in other words, they do not refer to a specific thing (noun), but a thing in general.
a / an
‘a’ = before a singular noun that begins with a consonant I have a car.
This car in not a specific car, so 'a' comes before the noun
‘an’ = before a singular noun that begins with a vowel I saw an airplane.
Definite articles (the) come before nouns that are definite and specific.
‘the’ = before singular and plural nouns I got the keys.
‘the’ = refers to a specific thing/person The new teacher is really strict.
‘the’ = to talk about old information the listener has already heard The movie was boring.
‘the’ = the thing/person has already been mentioned I read a news story. (first reference with ‘a’)
The story was interesting. (second reference with ‘the’)
'Zero' article simply refers to instances when nouns are not preceeded by an article.
‘zero article’ = to talk about something in general Students spend a lot of money on textbooks.