SubjectTo BeExamples
I | am | I am from New Zealand.
You | are | You are Chilean.
He | is | He is twenty years old.
She | is | She is a nurse.
It | is | It is a big dog.
We | are | We are intelligent.
You | are | You are students.
They | are | They are married.

Contractions of To Be are very frequent when we are speaking.

To BeContractionExamples
I am | I'm | I'm from New Zealand.
You are | You're | You're Chilean.
He is | He's | He's twenty years old.
She is | She's | She's a nurse.
It is | It's | It's a big dog.
We are | We're | We're intelligent.
You are | You're | You're students.
They are | They're | They're married.

The negative of To Be can be made by adding not after the verb.

SubjectTo BeExamples
I | am not | I am not from Spain.
You | are not | You are not Australian.
He | is not | He is not thirty years old.
She | is not | She is not a secretary.
It | is not | It is not a small cat.
We | are not | We are not stupid.
You | are not | You are not teachers.
They | are not | They are not single.

There are two ways of forming contractions of To Be in negative sentences. One is with a contraction of the subject and the verb (e.g. I am = I'm) OR a contraction of the verb and not (e.g. are not = aren't)

I'm not from Spain. | --- | --------------*
You're not Australian. | OR | You aren't Australian.
He's not thirty years old. | OR | He isn't thirty years old.
She's not a secretary. | OR | She isn't a secretary.
It's not a small cat. | OR | It isn't a small cat.
We're not stupid. | OR | We aren't stupid.
You're not teachers. | OR | You aren't teachers.
They're not single. | OR | They aren't single.

* Notice that the only possible contraction for I am not is I'm not.

To create questions with To Be, you put the Verb before the Subject.

Affirmative | You | are | happy.
  | Subject | Verb | 

Question | Are | you | happy?
  | Verb | Subject |  

AffirmativeQuestion
I am intelligent. | Am I intelligent?
You are a student. | Are you a student?
He is a pilot. | Is he a pilot?
She is from Spain. | Is she from Spain?
It is a big house. | Is it a big house?
We are ready. | Are we ready?
You are doctors. | Are you doctors?
They are rich. | Are they rich?

In spoken English, we usually give short answers in response to questions.

Are you a student? - Yes, I am (a student). The last part (a student) is not necessary. We use shorts answers to avoid repetition, when the meaning is clear.

QuestionShort Answers**Short Answers
Am I intelligent? | Yes, you are. | No, you aren't.
Are you a student? | Yes, I am. | No, I am not.
Is he a pilot? | Yes, he is. | No, he isn't.
Is she from Spain? | Yes, she is. | No, she isn't.
Is it a big house? | Yes, it is. | No, it isn't.
Are we ready? | Yes, we are. | No, we aren't.
Are you doctors? | Yes, we are. | No, we aren't.
Are they rich? | Yes, they are. | No, they aren't.

** With To Be, We don't use contractions in affirmative short answers unless there is additional information after it (in which case they are no longer considered short answers).