Auxiliary verbs, also known as helping verbs, are used with main verbs to form different tenses, voices, and moods. Examples include "is," "have," and "will." They help convey the time of an action, such as past, present, or future, and indicate aspects like continuous or perfect. They also form questions, negatives, and emphatic statements. For example, in the sentence "She is singing," "is" is the auxiliary verb indicating the present continuous tense.