1

Articles are small words that come before nouns. 'A' and 'An' are indefinite articles. We use them when we are talking about one general thing, not a specific one.

2

The rule for choosing between them is based on sound. Use 'A' before a noun that starts with a consonant sound, like 'a car'. Use 'An' before a noun that starts with a vowel sound, like 'an apple'.

3

'The' is the definite article. You use 'the' when you are talking about a specific thing that both the speaker and the listener know about. For example, 'Can you shut the door?' You also use 'the' when there is only one of something in the world, like 'the sun'.