Learn Finnish: Uusi laukku on kaapissa. - The new bag is in the closet.

This is due to consonant gradation, a very common spelling change in Finnish. When we add an ending that closes a syllable (like the "in" ending -ssa), double consonants like pp, kk, and tt simplify to single ones. Therefore, kaappi drops a 'p' to become kaapissa.

The word laukku has a double consonant (kk). Why doesn't it drop a 'k' in this sentence?

Consonant gradation usually happens when we add an ending to a word. Because laukku is the subject of this sentence, it is in its basic dictionary form and doesn't have an ending that triggers the change. If we wanted to say "in the bag," it would drop a 'k' and become laukussa.

How do we know it means "The new bag" and not "A new bag" if Finnish doesn't have words for "the" or "a"?

You rely on context and word order! In Finnish, when a location sentence starts with the subject (Uusi laukku), it usually refers to a specific thing we already know about, translating to "The new bag." If we wanted to introduce a new, unknown bag ("A new bag is in the closet"), we would flip the word order: Kaapissa on uusi laukku.

A quick refresher: why do we use -ssa for "in" instead of -ssä?