The difference between "can" and "be able to"

1. "Can" only be used in simple present tense(can) and simple past tense(could), while "be able to" can be used with model verbs together in any tense.

2. "Can" means normal ability, while "be able to" means you have ability to do something, means you will arrive at the result through your hard work.

3. In the simple past tense, "Could" means you have the ability, but you didn't finish something, while "was/were able to" means you did it trough your hard work, like "managed to".