SHORT ANSWERS

La risposta a una domanda può essere  "yes" oppure "no".  
Tuttavia in inglese è più corretto far seguire la semplice affermazione o negazione da una breve frase (SHORT ANSWERS).

PER RISPONDERE " SI' " si utilizza questa formula

YES, + PRONOME PERSONALE SOGGETTO + VERBO AUSILIARE/MODALE DELLA DOMANDA ALLA FORMA AFFERMATIVA NON CONTRATTA. 
are you a student? Yes, I am
sei uno studente? Sì, io sono.

PER RISPONDERE "NO" si utilizza questa formula

NO, + PRONOME PERSONALE SOGGETTO  + VERBO AUSILIARE/MODALE DELLA DOMANDA ALLA FORMA NEGATIVA. SI  PUÒ USARE LA FORMA CONTRATTA

Are you Italian? No, I am not.
Sei italiano? No io non sono

Altri esempi

Are you going to school? Yes, I am./ No, I am not.
Can you speak English? Yes, I can. / No, I can’t.
Did she come? Yes, she did. / No, she didn’t.
Is your son married? Yes, he is. / No, he isn’t.
Does John work hard? Yes, he does. / No, he doesn’t.
Is Peter your friend? Yes, he is. / No, he isn’t.
She is a nice girl. Yes, she is.
Joe has already come. Yes, he has.
He can speak English very well. Yes, he can.
The apples aren’t good. No, they aren’t.
She doesn’t like fish. No, she doesn’t.
They didn’t play well. No, they didn’t.
He is mad. No, he isn’t.
You are joking. No, I am not.
You can’t do it. Yes, I can.
He won’t come again. Yes, he will.
I didn’t break it. Yes, you did.