Auxiliary verbs are also known as helping verbs, because they help form compound conjugations, meaning compound tenses like the passé composé as well as compound moods like the past subjunctive.
With compound conjugations there are two verbs:
French has only two auxiliary verbs.
Whichever verb it is, the auxiliary is consistent for all compound conjugations: avoir verbs always take avoir as their auxiliary verb for all compound tenses and moods, while être verbs always take être. However, there are a few verbs that can take either auxiliary, depending on how they’re used: learn more.
Native French-speaking teachers teach être verbs by having students draw a house with a door, windows, at least two rooms, and a staircase, and then label it with the être verbs. For example, draw a figure passing in front of the house (passer), another entering it (entrer), and a third going upstairs (monter).
Check online for the verbs that come from the mneumonics.