In English grammar, countable nouns are individual people, animals, places, things, or ideas that we can count.
Look at the pictures above. Which words are countable nouns? Could you say why you think that?
You can put something into a container to count it, but the thing you are counting does not take the plural form. The container takes the plural form. For example: one carton of juice, two cartons of juice, three cartons of juice.