* a = indefinite article (not a specific _object_, one of a number of the same _object_s) 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 _object_s) 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.