One of the genuine surprises of beginner Mandarin: there is no general-purpose "yes" or "no". The language answers questions by echoing the verb.
The echo rule
A yes/no question contains a verb; the answer repeats it, positive or negated. 你去吗？ → 去 / 不去. 你喜欢中国菜吗？ → 喜欢 / 不喜欢. "Do you want coffee?" 你要咖啡吗？ → 要 / 不要. Whatever the question's main verb is, that is your answer.
The helper words
- 是 / 不是 - for is-it questions: 你是学生吗？ → 是 / 不是. Also 是的 / 对的 as free-standing "that's right".
- 对 - "correct", confirming a statement: 对，我是.
- 好 / 可以 / 行 - agreement to suggestions: 我们走吧 → 好.
- 没有 - the negative of 有 and of completed actions: 你去了吗？ → 没去 / 没有.
是 is not "yes"
The trap: answering 是 to 你去吗？ ("are you going?") means "is" - it answers nothing. Match the verb that was asked. For negation the two defaults split by tense: 不 for present/general (不吃 - don't/won't eat), 没 for completed (没吃 - didn't eat) and before 有 （没有）.
The grey middle
Real answers hedge constantly: 还行 (it's ok), 差不多 (more or less), 一般 (so-so), 不一定 (not necessarily), 再说吧 (let's see). The hedge vocabulary does more social work than yes or no - direct refusal reads harsher in Chinese than in English, so 可能不行 often IS the no.
Common questions
What is the word for yes in Chinese?
There is no single word - you echo the question's verb (去吗 → 去). 是/对 confirm statements, 好 accepts suggestions, but none is a universal yes.
How do you say no in Chinese?
By negating the verb asked: 不 + verb (不去), or 没有 for past/possession. 不是 negates "is". Blunter refusals are often softened to 可能不行 or 再说吧.
Is 是 yes or no?
Neither - it means "is/am/are". Used alone in answer to a 是-question it works like "yes", but it cannot answer a question about any other verb.