NOT A TEACHER
Hello, Gordham Sharma:
You have asked an excellent question. I hope that the links help you.
Here are a few points that I hope you find helpful:
1. Another name for "auxiliary verb" is "helping verb" because it helps the main verb.
a. Mr. X is a teacher. ("Is" is the main verb.)
b. Mr. X is eating. (This time "is" is an auxiliary verb. That is, if I said only "Mr. X eating," you would get the idea, but
I can "help" the main verb ("eating") by saying "is" or "was" or "will be."
c. I study English. ("study" is the main verb.)
i. Note how I can change the meaning by adding an auxiliary verb:
(a) I will study English.
(b) I can study English.
(c) I must study English.
2. A very important function of auxiliary verbs is to make questions and the negative.
a. "Tom loves grammar." We need an auxiliary to make a question:
Does Tom love grammar?
Should Tom love grammar?
b. And for the negative:
I do not know French.
He did not understand.
*****
Well, I think that you get the idea. If you have a question about a sentence that confuses you, just ask here in the "Ask a Teacher" forum. Many people are eager to help you.
HAVE A NICE DAY!
*One source I consulted was The Oxford Dictionary of English Grammar (1994) by Ms. Sylvia Chalker and Mr. Edmund Weiner.