When we are talking about one thing in particular, we use
the. When we are talking about one thing in general, we use a or an.
I heard the owl last night. ( = The owl we have already heard => a definite one )
I heard an owl last night. ( = an owl, it's not a definite one )
The capital of Italy is Rome.
I have bought the bag I wanted
Has he parked the car?
There isn't any milk in the fridge.
Please switch off the light of the bathroom
I was born in a village.
He had an orange juice for breakfast.
James ate a steak.
They want to have an armchair
Has your grandmother got a chair?
The red shoes
Read this short paragraph, it can help you :
A little girl ( = any little girl ) anda woman ( = any woman ) were walking in Lincoln Avenue. The little girl ( = the one I have talked about before ) saw a pair of shoes ( = non - definite ) in a shop ( = any shop ). She asked the woman ( = the woman I have mentioned ) if she could buy the shoes ( = the shoes she has seen ) for her. The woman ( = the woman is the one I have mentioned twice ) said: 'I don't think the red shoes ( = the shoes mentioned ) will suit you. Look ! There is a pair of blue shoes ( = another one ) at the back ( = there's only one back ) of the shop-window. ( = the shop-window they were looking at )'