"Do you need to use the hairdryer?" "Yes, I do."
Need you make so much noise?

In the first sentence above need to is not a modal auxiliaryA helping verb used with main verbs to express mood, voice and tense. E.g.: I can't stand when I am disturbed. ("can", "am"), and behaves like a main verbA verb that can express an action or state in itself. E.g.: John likes squash a lot. ("like"), similarly to have to. In the second sentence need is a modal auxiliary, which is used mainly in questions and negativeA declarative sentence indicating "no". E.g.: Tim has no friends. forms. Note that the affirmativeA declarative sentence indicating "yes"; also called a positive sentence. E.g.: John likes squash a lot. form of need can still be used after negative verbs and in sentences which express doubt, negative or restrictive ideas:

I don't think he need go just yet.
I doubt whether I need help you.
You need only have asked.

Both need and need to mean something like have to.

MUST and HAVE TO
Modals expressing present and future necessity / obligation SHALL