To be able to do something means to have the ability to do it. Be able to is sometimes used in place of can or could. Instead of, "I can't go," you might say, "I am not able to go."
You can use be able to in any tense. Just change the tense of the verb be. For example, you can say, "I was able to see a movie last night," or, "He will be able to visit me tomorrow."
Be able to Grammar Quiz
Be able to Lessons: