Learn Danish: Du må ikke ryge her. - You must not smoke here.

When you have a modal verb like må and a second verb like ryge, the word ikke goes between them. In a standard Danish main clause, ikke always comes immediately after the first (conjugated) verb, which pushes the second verb further back in the sentence.

Doesn't må usually mean "may" or "are allowed to"? Why does this mean "must not"?

You are right! By itself, må often means "may" or having permission. However, the combination må ikke specifically translates to "must not" or "not allowed to". It is the standard way to express a strict rule or prohibition in Danish.

Why is the verb ryge used here instead of the present tense ryger?

Because it follows a modal verb (må). Just like in English, modal verbs are always followed by the infinitive (dictionary) form of the main verb. Therefore, we drop the present tense -r ending and just use ryge.

What happens to the word order if I start the sentence with Her?

If you emphasize "here" by putting Her at the very beginning of the sentence, the Danish "verb-second" (V2) rule kicks in. The first verb (må) must stay in the second position, so the subject (du) swaps places with it: Her må du ikke ryge.