Articles, which can also be called determiners, modify and give information about nouns. There are two types of articles: a definite one and an indefinite one.

Definite Articles: "The" is used to modify specific or particular nouns and defines the noun.

"I'm driving to the shop."

Indefinite Articles: This is used to define a general, vague noun. For this type of article, we use "a" or "an".

"It's a cat."

"I'm planning to go to an event tonight.'

*The use of "a" and "an" is dependent upon if the first letter of the next word will be a vowel. If it's a vowel, use "an". If it's not a vowel, you need to use "a".

Zero article: There is no use of "a" or "an".

"Apples are green." ---> It's a generalized statement with no definite article being presented in the sentence.

"Oranges are orange." ---> This is only a reference to a noun.