e.g. a book, a cat, a camera, a university, a European
The article form “an” is used before a word (singular) beginning with a vowel (a, e, i, o, u) or consonant with vowel sound (or beginning with mute h ).
e.g. an apple, an elephant, an umbrella, an hour,
1. Before a singular noun which is countable
e.g. He bought a book
She is eating an apple.
2. Before a singular noun which refers to a class of things.
e.g. An orange is rich in vitamins.
3. Before a name of a profession
e.g. She wants to be a doctor
He is an engineer.
4. For certain expressions of quantity
e.g. a lot of, a few, a couple, a dozen
5. For certain numbers.
e.g. a hundred, a thousand, a million
6. Before a singular, countable noun in exclamation.
e.g. What a beautiful flower!
What a nice shirt!
7. Article a/an is not used before uncountable nouns
e.g. water, milk, sand etc
Emoticon