Kari has explained the words for you, so can I tell you something else? Your question should be this:
'What's the difference between these words?'
I think there must be a grammar book somewhere in China which is misleading students into thinking that 'among' must always be used when you are talking about three or more elements. Even advanced learners, who write otherwise faultless English, seem to believe that this is the case. In fact, if you distinguishing between elements individually, as you are here, the correct word is 'between', not 'among'. Whether you are asking us the difference between two or twenty things, the preposition is always 'between'.