Helping or auxiliary verbs allow us to create verb phrases. Without them we would have a hard time expressing exactly when something happened (tense), what the tone of the statement is (mood), and whether the action is active or passive (voice).
In addition, a subcategory of helping verbs (called modal auxiliaries) provides other nuances like possibility and necessity.
Three of the most common helping verbs come in quite a few forms (in grammatical terms, they are strongly inflected):
These helping verbs make it easy to create verb phrases:
have been talking
In a sentence, these phrases may be interrupted by adverbs:
You were not listening
I am fortunately going on holidays then.
Alternatively, in questions a helping verb may come before the subject:
Have you been taking your medication?
The only thing that never changes is that the helping verbs always come before the main verb.