Let's start with a very popular song from 1967:
We can put all the nouns into two groups:
countable nouns (= бројиве именице) - we can count them, they can be singular and plural, they can take the indefinite article, they answer the question How many:
I like apples.
An apple is a fruit.
uncountable (mass) nouns (= небројиве именице) - we can't count them (but, we can say two bottles of water or four pieces of furniture, for example), they are always singular, they can't take the indefinite article, they answer the question How much:
Milk is white.
No news is good news.