Learn Finnish: Kukaan ei laula. - Nobody is singing.

In Finnish, negative pronouns like kukaan always need to be paired with a negative verb like ei. You can think of it as a mandatory double negative: literally, nobody does not sing.

Why is the verb laula instead of laulaa?

Because this is a negative sentence. After the negative verb ei, the main verb drops its personal ending. A positive sentence would use laulaa (sings), but in the negative, that extra a is dropped to make the base form ei laula.

Is kukaan related to the word kuka (who)?

Yes! Kukaan is formed by taking the question word kuka (who) and adding the ending -an (which is a variation of the -kaan or -kään suffix). In negative sentences, this suffix turns who into anyone or nobody.

The current lesson is about negation of possession. Why aren't we using the -lla ending or the partitive case here?

Because this sentence doesn't express ownership. Negation of possession (like minulla ei ole autoa - I don't have a car) uses the -lla ending and the partitive case. But this sentence is just a simple action (Nobody is singing), so it uses the basic subject kukaan and a normal verb laula, with no partitive needed.