"A" and "AN"

We use a/an – the indefinite article – when we talk about something for the first time.

The article ‘a’ is used before a consonant word or any vowel with a consonant sound. 

Indefinite article ‘a’ examples:

1. A man is sitting on the chair.

2. She wore a uniform to school.

Similarly, the article ‘an’ is used before the words beginning with a vowel (a, e, i, o, u) or the letter of a consonant word with a vowel sound. 

Indefinite article ‘an’ examples:

1. She is an intelligent girl.

2. He is an honest boy.