Learn Finnish: Rannalla on vaaroja, kuten meduusoja ja roskia. - There are dangers on the beach, such as jellyfish and trash.

The word kuten (such as) acts as a bridge. The examples following it must match the grammatical case of the general category they belong to. Since the category vaaroja (dangers) is in the partitive plural, the examples meduusoja and roskia must also be in the partitive plural.

Why is the verb on (is) in the singular instead of the plural ovat (are), since there are multiple dangers?

This is a classic existential sentence (Location + on + Subject). In Finnish, when you state that something exists somewhere, the verb is always the singular on, even if the subject (vaaroja) is plural.

The English translation says "trash" (singular), so why is roskia plural?

In English, "trash" or "garbage" is usually an uncountable singular mass noun. In Finnish, roska refers to a single piece of trash. To talk about trash collectively or generally, you use the plural form, which is why we see the partitive plural roskia here.

Can I use esimerkiksi instead of kuten here?

Yes, you could say esimerkiksi meduusoja ja roskia (for example, jellyfish and trash). However, kuten specifically means "such as" or "like" and directly links the examples to the preceding noun vaaroja, making it a very natural fit for this kind of list.