The Chinese have two names – for example, Xu Zheng Xi or Wu Yifan. The surname comes first in order, followed by the personal name.
There are many surnames in China, the most popular are Li, Wang, Zheng, Zhou, etc. So, when meeting someone, if you are adults, they call either your surname or your full name. But you should address a person by last name if you are not close friends. For example, Miss Wang, Mr. Song, etc. This shows your respect for the other person.
Many young Chinese take additional English pseudonyms. For example, Wu Yifan’s English name is Chris Wu. If your interlocutor introduces himself by a Western name, then you can call him that (Alex, Jack, etc.), without a surname. The Chinese understand that it is difficult for foreigners to pronounce their names, so they take pseudonyms for themselves to make it easier to remember.