‘A‘ and ‘an‘ are used when we speak of a countable object for the first time.
Look at the picture 1.
We can see a pen, a laptop, a spade and a book.
Picture 2 shows nouns which go with ‘an’. We use ‘an’ for words beginning with vowel sounds.
We have an orange, an egg, an umbrella and an elephant.
A kangaroo was here just now.
The kangaroo has a joey.
The sun is shining.
Look at Picture 3.
We use ‘a‘ in front of ‘kangaroo’ in the first sentence.
In the second sentence, we use ‘the‘ in front.
‘The‘ is used when we want to speak of the same thing again.
Look at Picture 4.
We use ‘the‘ before ‘sun’. Why is this so?
We use ‘the‘ as there is only one sun.
‘The‘ is also used when there is only one such object.