Can vs Be Able to

BE ABLE TO is used when it's not possible to use CAN. For example, we cannot say "I will can do it", but "I will be able to do it".

It's important to say that that BE ABLE TO, as opposed to CAN, can be used in all past, present and future tenses.

There are other instances where CAN and BE ABLE TO are interchangeable: "I can cook" = "I am able to cook." In both examples an ability to do something is expressed, but the difference is in the register: CAN is used in normal, everyday English, while BE ABLE TO in more formal.