Present simple: be

Positive

I am fine, thanks. - I'm fine thanks.

You/We/They are students. - You're students.

He/She/It is in class 3A. - He's in class 3A.

Negative

I am not very well. - I'm not very well.

You/We/They are not students. - You aren't students.

He/She/It is not here. - He isn't here.

Use contractions in speaking.  Example: I'm glad to see you again.

Don't use contractions in positive short answers. Example: Yes, she is  NOT Yes, she's.

Question and short answers

- Am I married? 

- Yes, I am. / No, I'm not.

 - Are you/we/they tourist?

- You/we/they are.  /  You/we/they aren't. 

Use be + subject (I/you/he, etc) for the question.

Use be to say who a person is or what an object is: I'm James. It's a pen.

Use be to say where a person or a thing is from: She's American and He's Italian.

Use be to talk about people's jobs: I'm a student. My mother' a journalist.

Use be to talk about a person's age: I'm eighteen.

Use be to say where something is: The Eiffel Tower is in France.

Use be to say how much something is: It's twelve euros.