We use 'could' to talk about what someone was able to do in the past. It shows past ability or skill. It is like the past form of 'can'.
I could swim when I was five.
She could read simple books last year.
'Could' is used to ask for something politely or to offer help. It is softer and more polite than 'can'.
Could you help me, please?
Could I have some water?
'Could' is used in 'if' sentences to talk about something that might happen or be true if conditions are met. It shows possibility in imaginary situations.
If I tried, I could win the race.
She could be happy if she lived here.
'Could' shows that someone had permission to do something in the past. It means it was allowed or accepted then.
When I was young, I could watch TV late.
You could visit your friend yesterday.
'Could' is used to give a polite idea or suggestion. It shows what someone might do. It is softer than direct commands.
You could try the new restaurant.
We could watch a movie tonight.
'Could' shows a wish or regret about something that is not true now or in the past. It expresses desire for a different situation.
I wish I could fly.
He could have helped us yesterday.
