In the English language we have two kinds os articles.
Indefinite articles: A an AN. Are used to refer something.
I have a cat.
That is an elephant.
NOTE: We use A before words wich the first letter has a sound of a consonant.
We use AN before words wich the first letter has a sound of a vowel.
Definite articles: THE. Is used when you know that the listener knows or can
work out what particular person/thing you are talking about.