Learn Finnish: Kaapista puuttuu saippuoita. - Soaps are missing from the cabinet.

The base word is saippua (soap). When adding the partitive plural ending -ita to a word ending in -ua, the final a changes to o. This creates the form saippuoita (some soaps).

If multiple soaps are missing, why is the verb puuttuu in the singular?

This is a "state of being" or existential sentence, which tells us what exists (or is missing) somewhere. In these sentences, when the subject is in the partitive case (like saippuoita), the verb is always in the third-person singular (puuttuu), even if the English translation uses a plural verb.

Why is the word for cabinet in the -sta form (kaapista)?

The verb puuttua (to be missing) requires the location it is missing from to be expressed with a "from" case. Because a cabinet is an enclosed space, we use the elative ending -sta (from out of) rather than the outer ending -lta.

Why does kaapista have only one p when the basic word is kaappi?

This is a reminder of consonant gradation. Adding the ending -sta closes the final syllable, which forces the strong double pp in kaappi to weaken to a single p in kaapista.