Rule 1. If the word is countable, you must always put an article (a/an/my/his/etc.)
Rule 2. Also use if there are adjectives before the noun.
Ex: He drives an old car.
Rule 3. Never use a/an with plural words.
Ex: I asked her for advice. = ADVICE is uncountable.
Rule 4. Use THE to talk about specific things
Ex: I caught a train to London.=It doesn’t matter which train.
Ex: The train was late.=That particular train was late.
Rule 5. Often use A when we mention something for the first time, and then change to THE when it’s clear which thing we are talking about.
Ex: He was talking to a man.The man was laughing.
Rule 6. We also use THE when it is obvious which thing we are talking about or when there is only one of something.
Ex: Could you please shut the door.
Article expections
*We don’t use A/AN before the name of meal.(BREAKFAST/LUNCH/DINNER)
*We don’t use A/AN before words like school,prison,or college when we are talking about them in a general way.
*We use THE before the name of shops,or places where we go for service when they are the ones we usually go to.