sum=萨姆

as your english name is sumsum, you can use 萨萨 or 莎莎 as your chinese name, you can choose the one you like from it.

surnname+firstname. tradiontally,like me,name is 李文凯（liwenkai） 李 is my surnname，文 is provuded by my ancestor，（my farther‘s is 坤，and my son’s is 章（i haven't son right now，i am just student）），凯 is my parents give me。 someone‘s surnname maybe include two words，someone maybe give up ancestor’s “gift”。

Well, if you are looking for a Chinese name, translate your name into Chinese or just find a Chinese character with similar pronunciation would both be good options. But some people want to have more common Chinese name so they just picked a common surname and a common last name. Is your name sumsum? What's the meaning of this word?

I didn't get the exact meaning of your question, I will just try to answer it with my understanding. Chinese people put surname in front of the first name,and the first name normally have one or two words. If you want to translate an English name directly into Chinese, you need to find how many syllable does the English name have and then choose the same numbers of Chinese words with the same pronunciation.