Finnish vowels split into two groups that cannot share a word: back vowels a, o, u and front vowels ä, ö, y. Every ending you add must match the group already in the stem - talossa but metsässä. The vowels e and i are neutral and fit either.
Examples
- Asun talossa.
- I live in a house.
- Olemme metsässä.
- We're in the forest.
- Puhutko sinä suomea?
- Do you speak Finnish?
The mistake to avoid
This governs EVERY ending, including the question particle - so it is puhutko but syötkö.
Where this fits in
Numbers, days, time, Finnish A1: Count, talk about days and months, give the time, and handle numbers in real situations.