Learn Swedish: Flickan väntar på stationen där tåget stannar. - The girl waits at the station where the train stops.

In this sentence, där means "where." It links the main clause (Flickan väntar på stationen) to a relative clause that describes that specific place (där tåget stannar). It works exactly like "where" in English when describing locations.

Why do we use på instead of i for "at the station"?

In Swedish, you generally use på (on/at) rather than i (in) for public institutions, workplaces, and transport hubs. This includes places like stationen (the station), flygplatsen (the airport), and sjukhuset (the hospital).

I learned that väntar på means "waiting for". How do we know it means "waits at" here?

You are right that väntar på often means "waiting for" (for example, väntar på tåget means "waiting for the train"). However, because på is the standard preposition for being physically present at a station, context tells us she is waiting at the location, not waiting for the building itself to arrive!

Does där change the word order in the second half of the sentence?

No, it keeps the standard Subject-Verb word order (tåget stannar). The strict "verb second" rule you learned earlier applies to main clauses. Because där introduces a subordinate clause (a secondary clause that cannot stand alone), the subject comes right before the verb, just like in English.