In a sentence that has helping verbs, both English and most European languages can form questions by moving the helping verb before the subject. This is called inversion. However, though most European languages, including Norwegian, can do the same thing with a main verb that has no helping verbs, English cannot, except for the verb to be (as a main verb), or also 'have' in the UK. English makes us add the helping verb 'do' to make questions with those verbs using inversion, as it also requires us to use 'do' to make negatives. Thus: DO the men read the books? The men DO NOT read the books. It's a strange system compared to other European languages, but it's the one we're stuck with.