As the title, I would like to find out the different usage between "will be doing" "will do" ? ?

How to use the "will be doing" and "will do"?

I have read some of the leave are written in English such as"I will be out of office, sth ...", why not is "I will out of office..."?

Hello, jgong-- and welcome to English Forums.

The progressive aspect (-ing form) of verbs works similarly in all tenses, and has a similar relationship to the simple verb forms. Progressive is used to indicate a continuing activity, especially relative to the rest of the sentence:

I study English = generally, an activity I do at unspecified times
I am studying English = now or currently I am actively doing this.

I studied English = a past fact
I was studying English = I was doing this when something else happened: I was studying English when the earthquake struck.

I will study English = a future fact; sometime in the future I will do this.
I will be studying English = I will be doing this when something else happens: I will be studying English when you come to pick me up.

Another use of progressive aspect is for politeness or to show special interest in the action:

Were you really studying English with your girlfriend last night?
Will you be studying English in school next year, too?

I will out of office-- This is no good; it has no verb.
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thank you Mister Micawber

I will out of office - This is no good; it has no verb

so this "be" of "I will be out of office ..." in here as an auxiliary verb application?
No. It is the main verb and a linking verb.
Thank you very much
Er.I can understand some,also I need to study more...
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