(1) When talking about a skill or general ability in past, use could or be able to: ‘By the time she was four, she could/was able to swim in the whole the pool.’ (2) Used to politely ask for permission to do something: ‘Could I have the address please?’
When talking about a single event in the past, we usually use be able to or manage (NOT could): ‘Luckily, we managed to get there before the shops closed.’ ‘Were you able to start the car?’
