A verb is a word that expresses action or a state of being. In the sentence “The dog runs fast,” runs is the verb because it shows what the dog is doing. In “The cake smells delicious,” smells is the verb because it describes the cake's state.

Verbs are the engines of sentences. Without them, you can't really say anything is happening or existing. Think of nouns as the people and things in your mental movie, and verbs as everything those people and things do. “Sarah laughs.” “The storm approached.” “We believe you.” Each of these sentences needs its verb to make sense.

Verbs change form to show when something happens. Walk becomes walked for the past, walking for ongoing action, and will walk for the future. They also change to match their subject: “I run” but “he runs.”

Some verbs show obvious action: jump, throw, whisper, explode. Others are subtler: think, understand, seem, exist. The verb “to be” (am, is, are, was, were) might be the most important verb of all, since it connects a subject to what it is or what it's like: “She is happy.” “They were students.”

When teachers talk about strong writing, they often mean choosing powerful, specific verbs. Compare “The horse went quickly” with “The horse galloped.” That single verb change makes the whole sentence more vivid.