- We use A when we talk about something for the first time. We use THE if we mention it again
example: We've got a cat and a dog. The cat is black.
- we use THE when it's clear what we're talking about, perhaps because there is only one of them
example: Let's go to the park
- We use A to say what someone's job is.
example: My uncle is a taxi driver
- We don't use an article when we are making a generalisation.
I don't like spicy food --> NOT I don't like the spicy food.
We use a to mean 'per or 'in each
example: She earns 10 euros an hour