This document discusses the three main jobs of nouns within sentences: as subjects, complements, and objects of prepositions. It provides examples of nouns functioning as subjects, including the Aztec Empire, Tenochtitian, invaders, and Spanish soldiers. Complements are defined as words that complete the meaning of a verb, and can be predicate nouns, direct objects, or indirect objects. Finally, objects of prepositions are nouns that follow prepositions in sentences, and some commonly used prepositions are listed.