You already know that verbs express action or state of being. You also know that verbs have tense, mood, and voice.
Sometimes, to produce the various tenses, moods, and voices of verbs, you must use auxiliary verbs, or "helping" verbs. Remember that verbs only have five forms, so the auxiliary verbs or "helping" verbs allow us to form all of the various tense, moods, and voices.
Auxiliary verbs are used to form the perfect tenses and the future tense.
Auxiliary verbs are used to form the subjective mood, and can help to add emphasis with the imperative or indicative moods.
How auxiliary verbs help with voice:
Auxiliary verbs are used to form the passive voice.
“Be”的所有形式：am is are was were
“Have”的所有形式：have has had
其他词：can could shall should will would may might must