Verbs are words that express actions, occurrences, or states of being, serving as the core of a sentence by indicating what the subject does or what happens to it. They can describe physical actions (run, jump), mental actions (think, believe), or states of existence (is, seem). Verbs are essential for forming complete sentences, as they provide the necessary action or state that connects the subject to the rest of the sentence. They can change form to indicate tense (past, present, future), mood (indicative, imperative, subjunctive), voice (active, passive), and aspect (simple, continuous, perfect). For example, in the sentence “She runs daily,” the verb “runs” tells us what the subject, “she,” does, while also conveying the regularity of the action.