This document discusses function words and their roles in language. It defines function words as words that connect important information but add little meaning on their own. The document outlines the main categories of function words, including auxiliary verbs like do and be that help establish tense, prepositions like in and at that show spatial and temporal relationships, articles like a and the that indicate specificity of nouns, conjunctions like and and but that connect parts of sentences, and pronouns like I, you, and it that substitute or refer to other nouns.