what are aualliary  verbs?

Helping verbs are also known as auxiliary verbs.  They are the verbs that come before the main verb.  Though they have no meaning of their own, they are necessary for the grammatical structure of a sentence. Since they help the main verb, they are known as helping verbs. 

For example:  The cat is drinking milk. 

Here, the main verb is 'drinking'. and 'is' is the helping verb/auxiliary verb.