Learn German: Der Arzt muss leider hier warten. - Unfortunately, the doctor has to wait here.

This is a key rule for using modal verbs like müssen (must / have to). The modal verb takes the second position in the sentence and gets conjugated (muss), while the main action verb (warten) gets pushed to the very end in its original dictionary (infinitive) form.

Why is it muss and not müsst or müssen?

The subject is der Arzt (the doctor), which is third-person singular (like "he"). The modal verb müssen is irregular: the stem vowel changes from ü to u for the singular forms (ich, du, er/sie/es). Therefore, it becomes muss. There is also no -t ending because modal verbs don't use typical endings for the first and third person singular.

I know leider means "unfortunately". Could I put it at the beginning of the sentence like in English?

Yes, you can! You could say Leider muss der Arzt hier warten. But remember the strict German "verb second" rule. If you put leider in the first position, the conjugated verb muss must stay in the second position. As a result, the subject (der Arzt) is forced to move to the third position, right after the verb.

The translation says "has to wait", but doesn't muss mean "must"?