Meaning of a in English
1. used for talking about a single person or thing for the first time in a textbook or conversation, often not translated
There is a cat on the table. The cat[=It] is black and white.
2. used for referring to a general type of person or thing, not to a specific one, often not translated
I have a small camera.
Let's go to an Italian restaurant.
I have a headache.
3. used when expressing prices, rates, or measurements to mean the amount for each one; for every; per
This cheese costs $10 a kilo.
We have two Chinese classes a week.
She has two meals a day.
He goes to Paris twice a year.
4. used instead of the number ‘one’
an hour
a hundred mile
for a year
a kilogram of rice
a dozen egg
a slice of bread
a piece of cake