Learn Finnish: Muut nukkuvat. - The others are sleeping.

Muu means "other". Because the subject is plural ("the others"), we add the regular plural marker -t to make muut. When adjectives or words like muu describe plural nouns or act as plural subjects themselves, they must take this -t ending to match in number.

Why does the verb nukkuvat end in -vat?

The ending -vat is the third-person plural ("they") verb ending. Because muut (the others) is a plural subject, the verb must agree with it.

The "I" form of this verb is nukun (with one "k"). Why does nukkuvat keep the double "kk"?

This is consonant gradation in Type 1 verbs. The double kk weakens to a single k when the personal ending closes the syllable (like the -n in nukun). However, the -vat ending keeps the preceding syllable open (nuk-ku-vat), so the strong grade kk remains.

Where is the word for "the" in this sentence?

Finnish does not have articles like "the" or "a". The single word muut simply translates to "the others" or "others" depending on the context.