Learn Swedish: Kören måste sjunga tydligt. - The choir must sing clearly.

Tydligt (clearly) is an adverb describing how the choir must sing. In Swedish, you usually form an adverb by taking the adjective, which in this case is tydlig (clear), and adding a -t to the end.

Why isn't there an att (to) before sjunga?

Måste (must) is a modal verb, which means it helps set the mood of the sentence. In Swedish, just like in English, modal verbs are followed directly by the infinitive form of the main verb without using att. We say "must sing", not "must to sing".

Is the k in kören pronounced like a hard K?

No, because it is followed by ö, which is a "soft" vowel in Swedish. When k comes before a soft vowel, it softens and is pronounced with a "sh" or "tj" sound. It sounds similar to the "sh" in the English word "shirt".

What is the base noun for Kören?

The base word is en kör (a choir). Because it is an en-word, we add -en to the end to make it definite, creating kören (the choir).