Learn Finnish: Onko koira liassa? - Is the dog in the dirt?

The base word is lika (dirt). When we add the "in" ending -ssa, it closes the last syllable. This triggers consonant gradation, and the rule for a single k is that it completely drops out. So, lika becomes lia-, and then we add -ssa to get liassa.

Why are there two vowels together in the middle of liassa?

When the k drops out from lika due to consonant gradation, the i and the a end up right next to each other. You just pronounce them one after the other to form the new stem lia- before adding the ending.

Why is the ending -ssa instead of -ssä?

This is a great time for a vowel harmony refresher. The word lika contains the vowel a, which is a back vowel. Because the word has a back vowel, the ending must also use the back vowel a, making it -ssa.

How does onko make this a question?

The word on means "is". To turn a statement into a yes/no question, we attach the question particle -ko to the verb, creating onko. In Finnish, the word carrying this question particle must always be moved to the very front of the sentence.