A person is called by
1) his full name
or
2) his name only
or
3) his nickname / stage name / pen name / etc.
In case 1), you find the full name a set of 2 to 4 characters. If it's a set of 2 characters, then the first is the surname and the last is the name. e.g. 林美 (here 林 is the surname and 美 is the name). If it's a set of 3 characters, then the first one is the surname OR the first two is the surname (we call it a 'compound surname' in English, or ' 複姓 ' in Mandarin). e.g. 歐陽龍 / 欧阳龙 (here 歐陽 / 欧阳 is one of the known 'compound surnames' and 龙 is the name). e.g. 司馬光 / 司马光 (here 司馬 / 司马 is another of the known 'compound surnames' and 光 is the name). e.g. 李大同 (here 李 is an ordinary surname and 大同 is the name). e.g. 施欣欣 (here 施 is again an ordinary surname and 新欣 is the name). If it's a set of 4 characters, then the first two is the compound surname and the last two is the name. e.g. 司馬中原 / 司马中原 (here 司馬 / 司马 is the compound surname and 中原 is the name). e.g. 張簡士豪 / 张简士豪 (here 張簡 / 张简 is a known compound surname and 士豪 is the name)
In case 2), you find it a set of 2 characters mostly. e.g. 士豪 (here 士豪 is the name because 士 is not a surname or at least not a common surname nowadays), here we can only know his name but not his full name (maybe he is 林士豪 or 郭士豪 or 司馬士豪, we don't know) and suppose it him because it looks undoubtedly a boy name (it could be a girl name, though, in some extreme cases). You might have a question: why can't we just call 林美 (an undoubtedly girl name mentioned in the first paragraph) by her name 美? It simply doesn't exist in this language, not the custom I mean.