Articles are used to modify nouns and could be considered adjectives.
There are only three articles: a, an, the
Indefinite Articles – “a” and “an” are indefinite articles which refer to a noun when the noun is not specific and is singular in number.
Singular – A car was speeding down the road this morning.
Plural – Cars were speeding down the road this morning.
A vs AN
“An” is used instead of “a” when the beginning sound of the next word is a vowel sound, when the beginning sound of the next word is a consonant sound we use “a”.
Notice I said, vowel “sound” or consonant “sound”. Usually words that begin with a vowel, also begin with a vowel sound, and usually words that begin with a consonant, also begin with a consonant sound, but there are some exceptions.
Consider the following: Some words that begin with a consonant are pronounced with a vowel sound at the beginning. “Honest” and “honourable” both begin with a consonant; however, the consonant is silent (not pronounced) so we would say, “an honest man” NOT “a honest man”.
Another example is “European”, which begins with the vowel “e”, but is pronounced beginning with the consonant sound “y”. We would say “a European” NOT “an European”. There are other examples which you will discover in time.
*Note – When writing, the first time you mention something you may use “a”, because it is indefinite, but in later sentences, you would use “the” because now after mentioning it, it has become definite. I bought a car. The car is blue.