Form: be + ing (present participle)
Meaning: The progressive tenses give the idea that an action is in progressduring a particular time. The tenses say that an action begins before, is in progress during, and continues after another time or action.
PRESENT PROGRESSIVE

(a) He is sleeping right now.

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.

PAST PROGRESSIVE

(b) He was sleeping when I arrived.

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 PROGRESSIVE

(c) 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 be in progress at a particular time in the future. Probably his sleep will continue.