Learn Finnish: Myyjä kantaa uusia hedelmiä kojuun. - The vendor is carrying new fruits to the stall.

They are the object of the sentence, and the action of carrying is currently ongoing. In Finnish, if an action is continuous or if you are talking about an undefined amount (like "some new fruits"), the object takes the partitive case. Since there are multiple fruits, we use the partitive plural.

How do we get the partitive plural hedelmiä from the basic word hedelmä (fruit)?

To form the partitive plural, you need the plural marker -i- plus the partitive ending (in this case, -ä). When a word ends in -ä or -a with three or more syllables, that final vowel usually drops out to make room for the plural -i-. So, hedelmä drops its final -ä, adds the plural -i-, and then adds the partitive -ä, resulting in hedelmiä.

How is uusia formed from the basic word uusi (new)?

Words ending in -si can be a bit tricky. While the singular partitive looks quite different (uutta), the plural stem keeps the -s- and looks like uusi-. To make it partitive plural, you simply add the partitive ending -a to that stem, giving you uusia.

Why does the sentence use kojuun instead of just koju (stall)?