Learn French: Les passagers arrivent sur le quai. - The passengers arrive on the platform.

The -ent ending on French verbs in the "they" form is completely silent! You just pronounce the base of the word, meaning arrivent sounds exactly the same as the singular form, arrive.

Since this lesson is about venir (to come), could we say Les passagers viennent sur le quai?

You could, but it changes the focus. Arriver focuses on the action of reaching a destination (to arrive). Venir means "to come" toward the speaker. If you say ils viennent, it implies that you are already standing on the platform watching them come toward you!

Why do we use sur here?

Sur means "on". Just like in English where passengers arrive and wait "on" a platform, French uses sur le quai rather than dans (in) or à (at).

Is the final "s" in passagers silent?

Yes! In French, the final -s used to make nouns plural is almost always silent. When listening, you only know the word is plural because you hear the plural word for "the", which is les.