Count nouns can occur in the singular or the plural; i.e. they can be counted: a horse, two horses; one book, three books, etc. Mass (non-count or uncountable) nouns cannot be counted and do not occur in the plural or with a(n), e.g.: (some) gold, money, coffee, intelligence, advice, etc. In some cases mass nouns are convertible to count nouns, which are then equivalent in meaning to a mass noun preceded by a partitive expression, e.g.:
a coffee = a cup of coffee
a beer = a glass (can, pint, etc.) of beer
the wines of France = the varieties (kinds) of French wine