1. This sentence means: I am from the Chinese department. Or we could say 我是中文系的(学生), which is better to understand. 2. 回 means 回复， but we would rather say 会我个电话 instead of 回复我个电话. 3. When A looks for B, but B is not here and C is here, then C would ask A 你找A有什么事？It means: what do you want? If you like, I can take a message for B. What you've reffered is not a word to word translation, so you cannot take "message" as "事" directly.

When we use them to describe something or someone, they mean the same. But in some cases just as above written, 好看 has some wired usages..