A Noun can be the subject or object of a sentience.

[A noun is] any member of a class of words that can function as the main or only elements of subjects of verbs (A dog just barked), or of objects of verbs or prepositions (to send money from home), and that in English can take plural forms and possessive endings (Three of his buddies want to borrow Johns laptop). Nouns are often described as referring to persons, places, things, states, or qualities, and the word noun is itself often used as an attributive modifier, as in noun compound; noun group. [1]

Examples of nouns in sentences:

  1. Guns kill People.
  2. Elephants represent Republicans.
  3. The Solar System is in the Milky Way Galaxy.