We can use “Can” in order to say that something is possible or that someone has the ability to do something. Moreover, we can use can in order to say what we or other people can do in the present or future. But, it is important to note that there must be a base form of verb when we use “Can”.
Can has two forms such as can (present) and could (past)
I can swim (Present situation)
I can help you tomorrow. (Future)
Can you speak any foreign language?
The negative of can is can`t (or cannot)
We use “Could” in order to say something about the “Past”. This is no longer existing or true.
My grandmother could swim. (past, because now she cannot swim due to her age)
Be able to
“Be able to” is possible instead of “Can”. But you need to bear in mind that “Can” is more usual. We can use “Be able to” in order to express facts, things, or something else in the Past, Present and Future.
I am able to drive. (Present)
I was able to drive. (Past)
I will be able to drive. (Future)
Moreover, you need to know that we use “Be able to” when “can” has no present perfect, and when “can” has no infinitive.
I have not been able to sleep recently. (“can” has no present perfect )
Tim might not be able to come tomorrow. (“can” has no infinitive)