Learn Finnish: Paras dinosaurus on ehkä kasvinsyöjä. - The best dinosaur is perhaps a herbivore.

Paras means "best" and is the completely irregular superlative form of the adjective hyvä (good). Just like in English (good, better, best), Finnish uses hyvä, parempi, and paras.

If I wanted to talk about the best dinosaurs in the plural, how does paras change?

To make it plural, paras changes to parhaat. The hidden stem of paras is parhaa-, which you must use when adding any grammatical endings. So "the best dinosaurs" would be parhaat dinosaurukset.

How exactly is the compound word kasvinsyöjä built?

It is formed from kasvi (plant) put into the genitive form kasvin (of a plant), directly joined with syöjä (eater). Literally, it means "plant's eater".

Why is there no Finnish word for "a" before kasvinsyöjä?

Finnish does not have indefinite or definite articles like "a", "an", or "the". You simply translate the noun with or without an article based on what makes the most sense in the English context.