A-AN | Indefinite articles in English

How to use A and An, indefinite articles in English.
Indefinite articles in English are A and AN. They have the same meaning and the same function.
In English grammar, there are two articles: a, an. Indefinite articles are used before nouns or noun equivalents. The indefinite articles (a, an) are used before a noun that is general or when its identity is not known. There are certain situations in which a noun takes no indefinite article.
Indefinite article
A (before a singular noun beginning with a consonant sound)
AN (before a singular noun beginning with a vowel sound)
For the purposes of understanding how indefinite articles are used, it is important to know that nouns can be either countable (can be counted) or uncountable (indefinite in quantity and cannot be counted). In addition, count nouns are either singular (one) or plural (more than one). Noncount nouns are always in the singular form.
Use the indefinite article A or AN only with a singular countable noun. Use A before nouns that begin with a consonant sound, and use AN before nouns that begin with a vowel sound.
Sometimes an adjective comes between the article and the noun:
an unhappy boy, a red apple
The plural form of a or an is some. Use some to indicate an unspecified, limited amount (but more than one).
an apple, some apples