This document discusses the key components of a simple sentence, including subjects, verbs, and prepositional phrases. It defines subjects as answering "who or what is doing the action" and verbs as showing action or being. Helping verbs are described as verbs that come before the main verb. Prepositions are defined as small words that indicate position or possession, and prepositional phrases consist of a preposition and its object but are never the subject of a sentence. The document encourages practicing identifying these elements in sentences through an online activity.