Nouns can be used as the subject, direct object, and indirect object of a verb; the object of a preposition; and an adverb of adjective. Nouns also can show possession.
Subject: The mailcarrier always rings twice. Tulips are early spring flowers. (Tells who or what does or is something.)
Direct object: I finally sold my car. (Tells what is sold.)
Indirect object: Harold gave the cat another olive. (Tells to whom he gave the olive.)
Object of preposition: She gave directions over the phone. (Tells what is the object of the preposition over.)
Adverb: The train leaves today. (Tells when.)
Adjective: The office building faces the zoo. (Tells what kind, which one.)