They point out entities that can be counted, for example, five children, three rocks, thirteen euros.
Countable nouns are combined with plural quantifiers without being altered semantically.
The noun functions as the head of the subject. It is the main part of the subject.
The noun performs the function of direct object. It is a verbal modifier that represents the person, animal or thing that directly receives the action of the verb.
The nouns used in different sentences can perform different functions such as: circumstantial complement, agent, indirect modifier, predicative function, as an appositive, etc.