im wondering how to use YES NO

你朋友正確。

講中文時，所謂「係呀／唔係呀」係指「係呀，你句說話正確」或「唔係呀，你句說話不正確」，著眼點不在果句說話中提及果個動作。
甲：You can't cook.
乙：係呀（你講岩），I can't cook。
丙：唔係呀（你講錯），I can cook。

講英文時，個 Yes/No 則是按照回答時個動詞 verb 係 positive（can cook）定 negative（cannot cook）。無論阿甲問什麼、點問法，乙 can't cook 就永遠答 No，丙 can cook 就永遠答 Yes。個 Yes/No 可以說有點多餘呢。

甲：You can cook.
乙：No, I can't cook。
丙：Yes, I can cook。

甲：You can't cook.
乙：No, I can't cook。
丙：Yes, I can cook。　不過，丙在這裏也可能回答「No！死人甲！你錯了！」這不是正面回答甲的問題，所以唔算。

Before you are familiar with using yes 或 or no , you can do this to avoid confusion:

When your friend said you didn't know how to cook,
you can answer:
Yes, I do (you know how to cook)
or
No, I don't (you don't know how to cook).

This will shift the answer onto I do or I don't.