Auxiliaries, also known as auxiliary verbs, are verbs that help the main verb in a sentence by adding functional or grammatical meaning. They are used to form different tenses, moods, or voices of the main verb. Common examples of auxiliaries include be, have, and do. For instance, in the sentence "She is running," the auxiliary is helps indicate the present continuous tense. In addition to tense formation, auxiliaries can also express necessity, possibility, or permission. Modal auxiliaries, such as can, may, and must, are used to convey these meanings. For example, "You must finish your homework" uses the auxiliary must to express obligation.