The Verb TO BE

Probably the best known verb in the world: "To be or not to be..." 

Forms of To Be
	Present	Past	Perfect Form	Continuous Form
I	am	was	have / had been	am / was being
he / she / it	is	was	has / had been	is / was being
you / we / they	are	were	have / had been	are / were being

Normally we use the verb to be to show the status or characteristics 
of something or someone (as a stative verb). 
It says what I am, what you are or what something is.

Present Simple (stative)
I am a teacher.	You are a student.	He /She is a student.	It is a car.	We are all teachers.	They are  students.
Past Simple (stative)
I was a student.	You were a student.	He /She was a student.	It was a nice day yesterday.	We were all students once.	They were  students.
Future Simple (stative)
I will bea student.	You will be a teacher.	He / She will be a teacher.	It will be nice later.	We will be teachers.	They will be students.

When used with the present participle of other verbs 
it describes actions that are or were still continuing 
- auxiliary verb be [+ ing form of the main verb].

Present Continuous (active)
I am being silly.	You are being silly.	He /She is being silly.	It is being silly.	We are being silly.	They are being silly.
Past Continuous (active)
I was being silly.	You were being silly.	He /She was being silly.	It was being silly.	We were being silly.	They were being silly.

Am/Is/Are

The verb to be is used to create simple yes/no questions by simply inverting the order of subject and the “To be” verb.

For example:-

I am a teacher. (Statement)
Am I a teacher? (Question)

Question	Positive Statement	Negative Statement (possible short forms)
Singular
Am I ...?	I am ... (I'm ...)	I am not ... (I'm not ...)
Is he / she / it ...?	He / She / It is ...(He's/She's/It's ...)	He / She / It is not (He / She / It isn't... // He's / She's / It's not ...)
Are you ...?	You are ...(You're...)	You are not (You're not ...// You aren't...)
Am I being ...?	I am being ...	I am not being ... (I'm not being...)
Is he / she / it being...?	He / She / It is being ... (He's/She's/It's being ...)	He / She / It is not being ... (He / She / It isn't being...// He/she/it's not being...)
Are you being ...?	You are being ... (You're being ...)	You are not being ... (You're not being ... // You aren't being...)
Was I ...?	I was ...	I was not. ..
Was he / she / it ...?	He / She / It was ...	He / She / It was not ... (He / She / It wasn't)
Were you ...?	You were ...	You were not ... (You weren't ...)
Was I being ...?	I was being ...	I was not being (I wasn't being...)
Was he / she / it being...?	He / She / It was being ...	He / She / It was not being ... (He / She / It wasn't being... )
Were you being ...?	You were being ...	You were not being ... (You weren't being ...)
Will I be ...?	I will be ... (I'll be ...)	I will not be ... (I'll not be ...)
Will he / she / it be ...?	He / She / It will be ...(He'll / She'll / It'll be ...)	He / She / It will not be (He / She / It won't be ... // He'll not be / She'll not be / It'll not be ...)
Will you be ...?	You will be ...(You'll be ...)	You will not be (You won't be ... // You'll not be ...)
Plural
Are we / you / they?	We / You / They are (We're / You're / They're)	We / You /They are not (We're / You're / They're not // We / You / They aren't)
Are we / you / they being ...?	We / You / They are being ... (We're / You're / They're)	We / You /They are not being (We're / You're / They're not being // We / You / They aren't being)
Were we / you / they ...?	We / You / They were ...	We / You / They were not ... (We / You / They weren't ...)
Were we / you / they being ...?	We / You / They were being ...	We / You / They were not being ... (We / You / They weren't being ...)
Will we / you / they be ...?	We / You / They will be ...(We'll / You'll They'll be ...)	We / You / They will not be (We / You / They won't be ... // We'll / You'll They'll not be ...)

Examples

	Am/Are	Is
Question - ?	"Am I disturbing you?"	"Is this your coat"
Positive Answer - Yes	"Yes you are."	"Yes it is"
Negative Answer - No	"No you're not."	"No it isn't"
	Was / Were	Was
Question - ?	"Was I disturbing you?"	"Was that your old house?"
Positive Answer - Yes	"Yes you were ."	"Yes it was "
Negative Answer - No	"No you weren't."	"No it wasn't."

Note: The verb to be is also used when forming the passive voice.

*  The verb be is used in the following patterns:

1. with a noun:

My mother is a teacher.
Bill Clinton was the president of the US.

2. with an adjective:

This soup is very tasty.
The children were good.

2.1 with the -ing form to make the continuous aspect

We were walking down the street.
Everything was wet. It had been raining for hours.

2.2 with the -ed form to make the passive voice

The house was built in 1890.
The street is called Montagu Street.
This car was made in Japan.

3. with a prepositional phrase:

John and his wife are from Manchester.
The flowers are on the table.


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Source:http://www.learnenglish.de/grammar/verbtobe.html
http://learnenglish.britishcouncil.org/en/english-grammar/