We use a + consonant sound – a book, a hospital, a [ju:] university, a [ju:] uniform
We use an + vowel sound – an apple, an our, an eir, an interesting book, an [A] ugly toy
1. We use a/an with a singular noun when we mention something for the first:
I saw dog in the street. I bought pen and pencil yesterday.
2. One of many:
There is shop in my district. There’s new cinema in Al-Farabi street.
3. Any or it doesn’t matter which one:
Give me pen. Can you lend me copybook? I’m eating peach.
Five pounds (per) kilo. I go to the barber’s (every) once month. I drink two liters of water (every/each) day. I never drive at more than 100 kilometers (per) hour.
5. Description (who is who, what is what):
He is doctor. She is optimist. I’m journalist. It’s table. This is famous building.
6. To describe something or someone with to be or to exclaim:
That’s good book. It’s nice day today.
Such great day! What stupid mistake!
Such clever children! What awful whether!