Chinese uses measure words, a type of word called classifiers in linguistics which are common in East Asian languages. Measure words have a number of important uses, but one of the first ways you'll need to use them is for counting. Chinese learners should master them, starting with the measure word 个 (gè).
Whenever you talk about the quantity of something in Chinese, you need a measure word.
Number + Measure Word + Noun
English does actually have measure words, it's just that most nouns usually don't need them. In English, most nouns are count nouns - they specify one instance of something. "An apple," for example. Some nouns are mass nouns and refer to something without specifying how much of it there is. Examples are "furniture," "paper," "water," etc. You can't say "a furniture"; you need a measure word: "a piece of furniture," "two sheets of paper," "three glasses of water," and so on.
In Chinese, all nouns are mass nouns so they all need measure words. Just as in English, different nouns are associated with different measure words (e.g. it wouldn't make sense to talk about "a glass of furniture" unless something went horribly wrong in the factory).
Also remember that there isn't a one-to-one relationship between nouns and measure words. One measure word can be used with several different nouns:
And one noun can take different measure words in different situations: