We use be able + infinitive [to verb]. For example be able to go, be able to eat, be able to play, etc.
In this way, be able to has the same meaning as can.
 The negative forms of be able to are not able to (and) be unable to:
  • I am able to leave work early today.
  • Jack said he is not able to finish the report by 5:00pm.
  • I had to change my seat because I was unable to see the stage.
We use can + base verb, for example, can go, can eat, can play, etc. The negative forms are can not and can’t:
  • I can leave work early today.
  • Jack said he can’t finish the report by 5:00pm.
  • I had to change my seat because I could not see the stage.
When we talk about present ability, we use both be able and can, but can is more common:
  • I can speak English and German.
  • I am able to speak English and German.
  • Jack can cook French food.
  • Jack is able to cook French food.
When we talk about future ability, or use the present perfect, we only use be able.
  • You will be able to speak English well after spending two years at this school.
  • Someday, scientists will be able to communicate with dolphins.
  • Jack has been able to study English in the USA and in the UK.
  • I haven’t been able to call you because I’ve been busy at work.
When we talk about decisions or appointments in the future, we use both be able and can, but here too, can is more common:
  • I can meet you at the airport next week.
  • I am able to meet you at the airport next week
  • Sorry, I can’t come to the party tomorrow.
  • Sorry, I am not able to come to the party tomorrow.