"to be able to" and "can" have the same meaning.  CAN is used for present tense or present time only, but can be used for future if you mention the time period. For example:  I can call you tomorrow. Examples of present tense: I can swim.  He can understand. Also the negative: I can't go with you. But "to be able to" is used for more complex tenses or times.  He will be able to paint your house. (future)  I would not be able to work for more than 8 hours. (conditional) Would you be able to help us translate the book? (conditional + question)

I think "To be able to" is the infinitive form of "can." Can is the present indicative

for example:
Past tense: I could fly OR I was able to fly.
Present tense: I can fly OR I am able to fly.
Future tense: I will/shall be able to fly.
Subjunctive: If I could fly.... OR If I were able to fly....
Conditional: If I ate less food, I could fly. OR If I ate less food, I would be able to fly.
Present perfect: I have been able to fly.
Past perfect: I had been able to fly.

What is the difference.