A verb is that part of a sentence which talks of the state of action performed by or associated with the subject. A formal sentence is not possible without a verb. All the actions are described in terms of time-present, past and future. Hence, A verb gives the idea of time when the action is performed.
Broadly speaking, language is basically used to express actions associated with human and non-human existence, and verbs indicate the state of these actions.
The Constituents of a Verb
A verb occurs in a sentence in the form of one word or a group of words. Look at these sentences in which italicized part indicates verb.
(a) I go. (one-word verb)
(b) She has gone. (two-word verb)
(c) They might have gone. (three-word verb)
(d) He would have been going. (four-word verb)