Examples of helping verbs include "to have," "to do" or "to be." Also known as auxiliary verbs, helping verbs do not perform the primary action of a given sentence, but they help the primary verb.
Without helping verbs, many sentences do not make any sense. For example, in the sentence "She is writing a long essay," the third person present tense form of the verb "to be" (is) must precede the primary verb (writing). Modal helping verbs such as "can/could," "may/might" and "shall/should" must be added to primary verbs if the speaker wishes to indicate change (e.g. "You should not skip school.")