BE

1) be: progressive forms
I am being/you are being etc + adjective/noun

We can use this structure to talk about actions and behavior, but not usually to talk about feelings. Compare:
You're being stupid. (= You're doing stupid things.)
I was being very careful. (= I was doing something carefully.)
Who's being a silly baby, then?
I'm happy just now. (*not I'm being happy just now.)
I was very depressed when you phoned.(*not I was being very depressed...)
Note the difference between He's being sick (GB = He's vomiting) and He's sick (= He's ill)

2) be with auxiliary do
Normally, be is used without the auxiliary do:
I'm not often sick, (*not I don't often be sick.)

But do is used to make negative imperative sentences with be (when we tell somebody not to do something):
Don't be silly! Don't be such a nuisance!

And do be is used to begin emphatic imperatives:
Do be careful! Do be quiet, for God's sake!

In an informal style, people sometimes use do with be in one or two other structures which have a similar meaning to imperative sentences:
Why don't you be a good boy and sit down?
If you don't be quiet you'll go straight to bed.

3) be + infinitive
I am to... you are to... etc

a) plans and arrangements
We use this structure in a formal style to talk about plans and arrangements, especially when they are official:
The President is to visit Nigeria next month.
We are to get a 10 per cent wage rise in June.
I felt nervous because I was soon to leave home for the first time.

A perfect infinitive can be used to show that a planned event did not happen:
I was to have started work last week, but I changed my mind.

b) 'fate'
Another use is to talk about things which are/were 'hidden in the future', fated to happen:
I thought we were saying goodbye for ever. But we were to meet again, many years later, under very strange circumstances.

c) pre-conditions
The structure is common in jf-clauses, when the main clause expresses a pre-condition - something that must happen first if something else is to happen:
If we are to get there by lunchtime we had better hurry.
He knew he would have to work hard if he was to pass his exam.

d) orders
We also use the structure to give orders.Parents often use it when speaking to children:
You are to do your homework before you watch TV.
She can go to the party, but she's not to be back late.

be + passive infinitive
Be + passive infinitive is often used in notices and instructions. am/are/is (not) to be + past participle:
This cover is not to be removed.

Sometimes only the passive infinitive is used:
To be taken three times a day after meals, (on a medicine bottle).

Some other common expressions with be + passive infinitive:
There's nothing to be done.
She was nowhere to be found.
I looked out of the window, but there was nothing to be seen.

tenses
Note that this structure exists only in present and past tenses, not present perfect or future. We cannot say that somebody *has been to go somewhere, or *will be to go somewhere. Participle structures (*being to go) are not possible either.

Be and Have
a) physical conditions, etc
To talk about experiencing hunger, thirst, heat, cold and certain other common physical conditions we normally use be (or feel) + adjective, not have + noun.
Note the following expressions:
be hungry (not have hunger) be thirsty be warm
be hot be cold be sleepy be afraid Note also:
be right be wrong be lucky

b) age, height, weight, size and color
Be is also used to talk about age, height, length, weight, size, shape and color.
I'm nearly thirty, (*not I have nearly thirty.)
She is nearly my age.
He is six feet tall.
I wish I was ten kilos lighter.
The room is ten metres long.
What size are your shoes?
What color are his eyes?
She is the same height as her father.

Be heavy is not usually used in measuring expressions.
It weighs 37 kilos, (*not It's 37 kilos heavy.)