It is used to express an action in progress in the future. we don't know or care when it started and when it will finish. At some point or period in time, this action will be in progress:
I will be listening to music at 9 tomorrow.
She will be cleaning on Saturday afternoon.
It is used to express two or more actions in progress happening at the same time or overlapping in the future:
I will be dancing while you will be studying.