Apart from the fact that few and some are both quantifiers and determiners, both can be differentiated in a number of ways. Although both are used to quantify an indefinite number of objects, the word few is used to indicate objects that are small in quantity or number. For example, I was expecting a lot of people on my birthday, but very few people showed up. In contrast, the word some are used to quantify or indicate a larger quantity of an unknown number of objects.
In other words, some can be used to indicate a larger part of something that is not specified or known. For example, in the case of a twenty-person party, few might mean from 1 to 5, while some might go up to 10. Also, one needs to be very careful when attaching them to nouns. Mostly, some can be used for both countable and uncountable nouns, whereas few are used mainly for countable nouns and should not be used for uncountable nouns.