A student of mine mentioned a rule she had been taught. According to this rule, the word between is correctly used when there are only two things and the word among for more than two.
She can't decide between the candies.
She can't decide among the candies.
According to this fake rule, the first sentence suggests that there are only two candies to choose from. The second sentence suggests that there are more than two candies to choose from. Then there are a bunch of exceptions involving groups and relationships. I will not explain the exceptions, because it is easier to explain the two words correctly.
Unfortunately the rule is wrong. Even more unfortunately, it is commonly taught. The word (preposition) between is used when discussing specific, individual things even if there are more than two of them.
He had to choose between Disneyland, Ocean Park and the Rugby Sevens.
Grandfather Chu divided the candy between his four grandchildren.
Their time was divided between English, Chinese, and Putonghua lessons.
(Of course Putonghua is also a Chinese dialect, but common use in Hong Kong reserves the title for Cantonese.
Reference: A Dictionary of Hong Kong English)
The word (preposition) among is used when discussing general groups that aren't specific things. In general groups the exact number of things is not generally known. It is used to show how someone relates to less distinct groups of people or things.
He chose among the amusement parks.
Fear spread among the students as the teacher handed out the test.
Please note neither of the sentences above prevents there being two students or two amusement parks. It is just that the number of them is not known. If the speaker knew that there were two amusement parks, the word between would be used instead of among.
The use of between and among also applies to location and direction. These two sentences describe where Mary walked.
Mary walked between the cars.
Mary walked among the cars.
The first sentence refers to specific cars. Possibly there are only two cars, but probably not very many. The second sentence describes someone wandering around a large number of cars possibly in a parking lot. If you know the exact number of cars use the word between. If there are many cars, and you don't know how many, use the word among.
Very often by following the fake rule about two things, or more than two things, students will by accident use the words correctly much of the time. Most random examples of the use of the word between will be with two specific things.
At the first table, Anne sat between Jane and Albert.
Mary sat among the boys.
At the last table, Mary sat between the boys.
It is physically difficult to sit between more than two people at a table. In the first sentence, if we have someone sitting on the table, or behind Anne's back, then they are not sitting at the table. (They could be across the table, but then they would not be next to Anne.) In the second sentence there are an unspecified number of boys. The sentence would still be correct for two, if the writer didn't know that there were two of them. In the third sentence these are specific boys and physical circumstances means that there are likely only two of them.
The use of between and among is very different than a choice of using two or more. The difference is between specific and general things. If you know that there are two, three or four things, then then use between. If you use the word 'many', instead of a specific number, use the word among. It is easier to understand how to use these words correctly, rather than to try to memorise some exceptions involving groups and relationships.