Articles
a, an / the
The words a/an and the are "articles". We divide them into "indefinite" and "definite" like this:
indefinite articles
definite article
a
an
the
We use "indefinite" to mean not sure, not certain. "Indefinite" is general.
We use "definite" to mean sure, certain. "Definite" is particular.
When we are talking about one thing in general, we use a or