What is the difference between the subject and a noun?

A noun is a Word for a person, a place, or a thing. A noun is used for the subject of a sentence or clause and the object of a verb or a preposition.

The subject is what the sentence is about. The subject of a sentence can be a noun or a pronoun (a Word that takes the place of a noun); a single Word or a group of Words. For Example:

John ran home. ('John' is a proper noun, a person's name, the subject of the sentence.)

The crying child ran home. (The noun 'child' is the subject of the sentence; the noun phrase 'the crying child' is the complete subject of the sentence.)

He ran home. (The pronoun he is taking the place of the noun John, or the noun child; 'he' is the subject of the sentence.)

A boy with a book in his hand ran home. (The noun 'boy' is the subject of the sentence; 'a boy with a book in his hand' is the complete subject.)

The noun 'home' is the object of all of the sentences.

In the last sentence, the noun 'book' is the object of the preposition 'with', and the noun 'hand' is the object of the preposition 'in'.