A verb is the word that names what someone does or what happens: run, eat, sleep. In The dog barks at the mail carrier, barks is the verb.
Not every verb shows action; some describe states or feelings, like seem or know.
The same is true in a kitchen scene. In Stir the soup while I set the table., the words stir and set are the verbs, because they name the doing. The soup and the table just sit there; the verbs are what people actually act out.
Now picture a stormy afternoon and the same contrast in one more sentence pair. In The rain is flooding the street again, flooding is the verb, something the rain is doing right now. And in The street seems quiet after the storm, seems is still the verb, even though it reports a state rather than an action.
A nearby word people mix up with verb is noun, the name of a person, place, or thing. In The cook chops onions, cook and onions are nouns; chops is the verb, the word that names the doing.
A safer check than any single trick: ask whether the word names the doing in that sentence. Careful, because cook itself can be either. In The cook chops onions it names a person, but in They cook dinner it names the action, so it is the verb there.