CAN VS BE ABLE TO

CAN: is a modal verb. We can not use in all tenses. It express ability, polite request, possibility, opportunity, and permission.

BE ABLE TO: is not a modal verb. We can use with all tenses. it express ability.

EXAMPLES:

I can sing. (I am a profesional singer)
I am able to sing.(I am a professional singer.I have to sing in a concert in that moment I lost my voice and I do not sing at the moment however I am able to to sing and the end  )