ARTICLES A AN and THE

• a = indefinite article (not a specific object, one of a number of the same objects) with consonants

She has a dog.
I work in a factory.

• an = indefinite article (not a specific object, one of a number of the same objects) with vowels (a,e,i,o,u)

Can I have an apple?
She is an English teacher.

• the = definite article (a specific object that both the person speaking and the listener know)

The car over there is fast.
The teacher is very good, isn't he?

• The first time you speak of something use "a or an", the next time you repeat that object use "the". 

I live in a house. The house is quite old and has four bedrooms.
I ate in a Chinese restaurant. The restaurant was very good.

• DO NOT use an article with countries, states, counties or provinces, lakes and mountains except when the country is a collection of states such as "The United States".

He lives in Washington near Mount Rainier.
They live in northern British Columbia.

• Use an article with bodies of water, oceans and seas - 

My country borders on the Pacific Ocean

• DO NOT use an article when you are speaking about things in general 

I like Russian tea.
She likes reading books.

• DO NOT use an article when you are speaking about meals, places, and transport

He has breakfast at home.
I go to university.
He comes to work by taxi.