Just like saying no, there are several ways to say “yes” in Chinese. How you say it really depends on the situation that you are speaking in. For example, if you answer yes to a question about whether you have something, it will be different from your yes answer to a question about whether you want something.
In the most general sense, the word 是 (shi4) can be used to mean yes. It literally means it is, which is the correct way to say yes when answering a question about a fact or event. For example, if someone asks you whether the meeting for tomorrow was changed from 8 am to 9 am, you can say 是 (shi4).
Similar to 是 (shi4) is 对 (dui4), which literally means correct. This is appropriate for yes/no questions as well.
If you are asked something else, such as whether you want something (要不要, yao4 bu2 yao4), you will answer with 要 (yao4), which means want. In context, it means “I want it”. This is the case for most other verbs. In the case of the questions 有没有 (you3 mei2 you3), meaning is there; 在不在 (zai4 bu2 zai4), meaning are you [at a place]; or 吃不吃 (chi1 bu4 chi1), meaning will you eat, the concept is the same. For these questions, if you want to say yes you should say 有 (you3), 在 (zai4), or 吃 (chi1) to mean, respectively, that there are, you are at the place, and you will eat. For these and most other verbs, it does not make sense to directly answer the question by saying 是 (shi4).
It is a bit confusing when you first learn it, but you can definitely learn it! Most of the time, you can just repeat the verb that is used in the question. If someone asks whether you went somewhere (你去了吗 ni3 qu4 le1 ma1), you answer I went (我去了 wo1 qu4 le1). If they ask you whether you like hot dogs （你喜欢不喜欢热狗 ni3 xi3 huan1 bu4 xi3 huan1 re4 gou3), you answer I like (我喜欢 wo1 xi3 huan1).
