This is a generalization, but between is for 2 things and among is for more than two. There are some cases where this rule is useless. Your title should be "what's the difference between between and among".

Among = (also amongst) is a preposition.In your question it means surrounded by something. "To work among the poor" Between = is also a preposition. In this question it means in or into the space separating two or more points, objects or people. "The baby crawled between her father's legs."

The preposition among means in the company of, by the joint action of, or each with the other. The preposition between means by the common action of, in point of comparison to, from one to another, or by the combined effort of.