The document discusses the major classes of verbs in English: full verbs, primary verbs, and modal auxiliary verbs. Full verbs can act only as main verbs, modal auxiliaries can act only as auxiliary verbs, and primary verbs like "be" and "have" can act as either main verbs or auxiliary verbs. The functions of different verb forms like the base form, -s form, -ing participle, and -ed participle are also outlined. Operators like auxiliary verbs can carry tense, negation, and questioning.