We can express our ability to do something by using can or be able to. These structures are usually interchangeable.

She can sing well. OR She is able to sing well.
He can ride a bicycle.
I can play the violin.

She can speak French.
My aunt can make delicious cakes.
My mother can knit beautiful sweaters.
My brother is able to walk on his hands.
My sister can make beautiful paper cranes.
My grandmother is 80, but she can still read without glasses.
She is able to write good English.
The baby is able to walk without support.
She can speak good English.

Cases where can is preferred

Use can when you want to say that you know how to do something.

She can swim like a mermaid. (= She knows how to swim like a mermaid.)
He can drive four wheelers. (= He knows how to drive four wheelers.)
My brother can paint beautiful scenery. (= My brother knows how to paint beautiful scenery.)

Cases where be able to is preferred

Be able to is preferred in cases where can / could are not grammatically possible. For example, we cannot use can or could in sentences in the present perfect or future tense.

She will be able to regain her confidence. (NOT She will can regain her confidence.)

I will be able to get a raise.
He will be able to solve this problem.
We will be able to reach there on time. (NOT We will can reach there on time.)
I have not been able to solve this problem.