The Continuous forms
FORM: be + -ing (present participle)
MEANING: The progressive tenses give the idea that an action is in progress during a particular time. The tenses say that an action begins before, is in progress during, and continues after another time or action.
He went to sleep at 10:00 tonight. It is now 11:00 and he is still asleep. His sleep began in the past, is in progress at the present time, and probably will continue.
He went to sleep at 10:00 last night. I arrived at 11:00. He was still asleep. His sleep began before and was in progress at a particular time in the past. It probably continued.
Future Continuous / Future Progressive
He will be sleeping when we arrive.
He will go to sleep at 10:00 tomorrow night. We will arrive at 11:00. The action of sleeping will begin before we arrive and it will in progress at a particular time in the future. Probably his sleep will continue.