How to get the differences between collective noun and noun of multitude ?

Found this :When used as nouns, collective noun means a noun which, though singular, refers to a group of things or animals. examples: a school of fish, a pride of lions, whereas noun of multitude means the name of something that contains many individual things or people.
And found this site

The way to spot the difference would be that a collective noun is used with a singular verb and a noun of multitude is used with a plural verb. “Noun of multitude” is really a collective noun used with a slightly different meaning (emphasis on the constituents of the collective), it’s not a separate class (in other words, the same word could be classified as either depending on the usage).

@Demosthenes, what if you don’t have a sentence, just the noun, and you’re trying to figure out which verb to use? Let’s say maybe you’re an English learner doing your homework and you need a guide. No doubt you’d be learning this in a different way from the way native speakers acquire it.

Isn’t this also a point of difference between British and American English?

@Jeruba It is. In British English, one could say something like the team have finished the project, which sounds odd in American English. If you’re learning American English, then I would say the singular is the more common usage; the plural is only used in a special semantic situation where you want to emphasize the individuals within the collective (which seems to be less frequently done).