The document discusses the importance of understanding sentence structure and the functions of words in context. It explains that there are four main functions - nominal, adjectival, adverbial, and verbal. Nominals include nouns, pronouns, and noun phrases. Adjectivals include adjectives and phrases that modify nouns. Adverbials modify verbs and adjectives and include adverbs and prepositional phrases. Verbals include main verbs and verbs combined with auxiliaries. Understanding functions provides insight into how words combine to form meaningful sentences.