Learn Finnish: Huoneessa on kaksi ikkunaa. - There are two windows in the room.

This is a classic Finnish "existential sentence" (expressing that something exists somewhere). In these sentences, the verb is always in the singular third-person form (on), even if there are multiple things, like the two windows here.

Why is the word for window (ikkuna) written as ikkunaa?

In Finnish, any noun that directly follows a number greater than one must be in the partitive singular case. Since we have kaksi (two), ikkuna takes the partitive ending -a to become ikkunaa.

The basic word for room is huone. Why does it have a double 'e' in huoneessa?

Finnish words that end in -e in their dictionary form usually add another -e before you attach most endings. So, huone turns into the stem huonee-, and then we add the "in" ending (-ssa) to make huoneessa.

Why does the sentence start with huoneessa (in the room) instead of a word for "there"?

Finnish doesn't use placeholder words like "there" in "there are". To say "there are X in Y", Finnish starts with the location (Huoneessa), puts the verb (on) in the middle, and ends with the things that exist there (kaksi ikkunaa).