I've come across a lot compunds of kanji where the kanjis mean the same thing. For example, 状態=state, 態=state, 状=state 表面=surface, 表=surface, 面=surface,mask Can someone explain how these two kanji compounds work and how do the meanings of the kanjis interact?
Compound words are made of kanji, but each kanji is not necessarily "words" that can be used on its own. Consider, in English, telepathy is made of tele- and -pathy, both of which have some meanings. But that does not mean you can use "tele" or "pathy" as a standalone word in a sentence. On the other hand, network is made of net and work, and both can be used also as standalone words.
Likewise, in Japanese, many kanji do not make much sense if used on their own. Each time you see a new kanji, you have to remember whether it is a true word or "just a character with some meaning".
- 状: It's not usable as a word. It's used only as part of compounds (性状, 状況, 異状, etc).
- 態: It's rarely used as a word. It means "voice" as in "passive voice" in linguistic contexts, but it's rare.
- 表: It means "chart/table/spreadsheet", but not "surface", as a standalone word.
- 面: It has many meanings as a standalone word (see your dictionary). Note that 表面 means "outside surface" but 面 as a word is more generic and can also refer to 裏面 and 内面.
Sometimes, very similar two kanji are compounded just to make the word longer. This is necessary because the on-reading of each kanji is short and there are many kanji with the same on-reading (for example, there are dozens of kanji that is read じょう; 情, 上, 城, 錠, 条, ...). See: If 校 is the kanji for school, why do I need 学 to actually say school?, What's the difference between 重責 and 責任? and Contribution of 気 to the meaning, for example, 勇気 and 勇.