To say an action will already be happening at a moment later on, use will be + the -ing form. It pictures the action in the middle of going on at that future time.
will be + the -ing form
This time tomorrow, I will be flying to Paris.
At 8 PM we will be having dinner.
Don't call at six. I will be working then.
Try it: Come at nine. By then we ___ breakfast. (will be having / will have / will be have) Answer: will be having — You're picturing the meal already in progress at nine, so use will be + the -ing form: will be having. "Will have" just says it happens, not that it's going on at that moment. And after will be you need the -ing form, not the plain "have".
won't be + the -ing form
For the negative, use won't be + the -ing form. (won't = will not.) The be and the -ing form stay the same.
I won't be working this weekend.
They won't be sleeping at midnight, the party only starts at eleven.
She won't be coming to the meeting, she's away.
Try it: Feel free to call after ten. I ___ by then. (won't be working / won't working / won't be work) Answer: won't be working — The negative keeps be: won't be + the -ing form, so won't be working. "Won't working" drops the be, and "won't be work" uses the base verb instead of the -ing form.
Will you be ...?
To ask, put Will first: Will + person + be + the -ing form. (It can also be a gentle way to ask about someone's plans.)
Will you be using the car tonight?
Will they be staying for dinner?
Will she be joining us later?
Try it: ___ you be using the printer this afternoon? I'd like to borrow it. (Will / Do / Are) Answer: Will — To ask about an action in progress later, start with Will: Will you be using it? "Do you be using" and "Are you be using" are not real forms. This one uses Will + be + the -ing form.
Try it: It's 6 PM now. At 8 PM the dinner will be going on. Which sentence shows the meal in progress at 8? (At 8 we will be eating, so don't call then. / At 8 we will eat, so don't call then. / At 8 we will be eat, so don't call then.) Answer: At 8 we will be eating, so don't call then. — You're picturing the meal in the middle of happening at 8, so use will be + the -ing form: will be eating. "Will eat" just says it happens, not that it's going on at that moment, and "will be eat" uses the base verb instead of the -ing form.