A verb is a word that indicates an action (jump, eat, work etc.), an event (happen, rain), or a physical/mental state (smell, like, seem.) These are all full verbs, i.e. They mean something in their own right. Other verbs are called auxiliary or "helping" verbs; these are only there to "help" complete the sentence and have no intrinsic meaning.Examples are the verb to be ("I am cold"), have ("I have eaten") and do "Where do you live?" There is sometimes confusion because the above verbs can be both full verbs and auxiliaries; that's why you get sentences like "He has had dinner" and "We don't do anything." Another category of auxiliaries is called modals; these are verbs like can must, will etc, and indicate the mood of the speaker or how s/he feels about the action. If you're not sure what kind of verb you're looking at, try saying it as a one-word imperative. If it communicates a message, however basic (e.g. "Go!") it's almost certainly a full verb. If it means nothing without a context, ("Shall!") it's an auxiliary.
