The main verb is the one the tells you the main action the subject does or the condition of the subject. The helping verb adds more information, such as tense or negation, etc. "Have," "do," and "be," are three helping verbs that can also be main verbs.
"He drives a large car." (Drive is the main verb.)
"He is driving a large car." (Drive is still the main verb. Is is the helping verb. )
He has a car. (Has is the main verb.)
He has crashed his car. (Crash is the main verb. Has is the helping verb)