FORMULA
 +/ - / ?
am/ is / are + Ving
 
FORM
Affirmative sentences: am/is/are + Ving 
I am Ving  I am working
We are Ving  We are working
You are Ving  You are working
They are Ving  They are working
He is Ving  He is working
She is Ving  She is working
It is Ving  It is working
Negative sentences: am/is/are + not + Ving 
I am not Ving  I am not working
We are not Ving  We are not working
You are not Ving  You are not working
They are not Ving  They are not working
He is not Ving  He is not working
She is not Ving  She is not working
It is not Ving  It is not working
I am not = I'm not (not: I amn't !)
are not = aren't
is not = isn't
Interrogative sentences: ... am/is/are + S + Ving … ?
(QW) am/is/are  S Ving (what/where/when) ?
  Am I working   ?
  Are we working   ?
Where are you working  now ?
  Are they working  at the moment ?
  Is he working   ?
Why is she working  this week ?
  Is it working   ?
Short answers:
 
Yes, S + am / is / are. 
No, S + isn't/aren't. (No, I'm not.)
Yes, I am.    No, I'm not.
Yes, we are.   No, we aren't.
Yes, you are.   No, you aren't.
Yes, they are.   No, they aren't.
Yes, he is.   No, he isn't.
Yes, she is.   No, she isn't.
Yes, it is.   No, it
isn't.
Note: In short answers we use pronouns (I, we, you, they, he, she, it)
- Is Mary working this week?
- No, she isn't.
(Not: No, Mary isn't.) 
***
V - verb (the infinitive without "to")
S - subject
QW - question word