Can, could, be able to (ability and possibility)

Can / Could
I can speak Spanish very well.
She could play the violin when she was three.
Could you open that door, please?
Can is a modal verb. It only has a present, past, and conditional form (but can also be used with a future meaning).
For other tenses and forms use be able to.

Be able to + Infinitive
I am able to accept your invitation.
They weren't able to come.
I'll be able to practise my English in London.
I'd like to be able to ski.
You can use be able to in the present, past, future, present perfect, and as a gerund or infinitive.
Be able to in the present and past is more formal than can/could.