Articles - The / A / An
There are only three articles in the English language: a, an and the.
Their actual use is a complex one especially when you get into the advanced use of English. Quite often you have to work by what sounds right, which can be frustrating for a learner.
We usually use no article to talk about things in general - the doesn't mean all.
"Books are expensive." = (All books are expensive.)
"The books are expensive." = (Not all books are expensive, just the ones I'm talking about.)
A and an
A and an are the indefinite articles. They refer to something not specifically known to the person you are communicating with.
You use a when the noun you are referring to begins with a consonant.
You use an when the noun you are referring to begins with a vowel.
"I saw an elephant at the zoo."
"I ate a banana for lunch."
You use the when you know that the listener knows or can work out what particular person/thing you are talking about.
"The apple you ate was rotten."
"Did you lock the car?"
You should also use the when you have already mentioned the thing you are talking about.
"She's got two children; a girl and a boy. The girl's eight and the boy's fourteen."
We also use the when we know there is only one of a particular thing.
the sun, the wind, the world, the North Pole etc..
However if you want to describe a particular instance of these you should use a/an.
"I could hear the wind." / "There's a cold wind blowing."
"What are your plans for the future?" / "She has a promising future ahead of her."
Do you want to know more about the use of English grammar? Read our recommended grammar books section.