certain＝concrete(具體). there are specific people. some＝abstract(抽象). there are some people, but we may not know who.

Mizzy gave a good explanation. I try to make it very simple: Some = several of whatever Certain = something specific I have some money, but a certain amount I like to keep to to buy food.

Both are used to refer to an unspecified quantity but with 'certain' the sense is that although the 'men' are not specified or identified they are assumed to be known. As a general statement 'some men' would be better.

Well that is an interesting question.Certain men referes to only specific kind of men for example men that are obsessed with coffee they are certain men among others that don't.Some men probably refers to only a specific people is just that both refer to the same thing it all depends on how it is used. :)