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describe nouns, i.e. make it clear what a noun refers to. For example:

I bought a jacket and a shirt.
My house is near the center.
There’s a lot of flowers in the garden.
She’s got two sisters and a younger brother.

You can’t use singular countable nouns alone, i.e. without a/the/my, etc.

We can’t get into the house without a key. (not key)
I want a banana. (not banana)
Paris is an interesting city.

A/an

We use ‘a’ and ‘an’ with singular countable nouns when we do not need to make clear
which person or thing we are talking about:

an accident, a banana, a couch, a dream, a neighbourhood.

Learn more about using a/an with nouns 

here

.

The

When people can understand which person or thing we mean, we use ‘the‘ with singular
and plural countable nouns:

The pie won the prize but the judges didn’t like the cookies.

Learn more about using the with nouns 

here

.

No Article

We use no article (the so-called ‘

zero article

‘) with plural countable nouns and with

uncountable nouns when we are talking in general:

Dogs usually don’t like cats.
Good health is more important than money.

Unlike singular countable nouns, plural countable nouns can be used alone: