Odotan junaa asemalla, koska bussi on myöhässä.

Because odottaa (to wait for) normally takes a partitive object: odottaa jotakin.
So odotan junaa is the standard way to say I’m waiting for the train. This is true even if you mean a specific train; it’s just how the verb typically governs its object in Finnish.

Asemalla is the adessive case (-lla/-llä), which often means on/at a place.
So asemalla = at the station (location “at” a place, not inside it).

Yes, but it changes the nuance:

• asemalla (adessive) = at the station (the station area/location)
• asemassa (inessive) = in the station (inside the building, more “indoors”)

In everyday Finnish, asemalla is very common for at the station in the general sense.

Finnish doesn’t have a separate grammatical form like the English present continuous. The simple present often covers “right now” actions:

• Odotan junaa. can mean I wait for the train or I’m waiting for the train, depending on context.

Odottaa is the infinitive (to wait). The present tense forms include:

• (minä) odotan = I wait / I’m waiting
• hän odottaa = he/she waits

Notice the change tt → t in odotan. That’s a common Finnish pattern (consonant gradation) in many verbs.

In Finnish, you normally put a comma before a subordinate clause introduced by words like koska (because):

• Odotan junaa asemalla, koska bussi on myöhässä.

This is more strict than in English, where commas with because are optional and meaning-dependent.

Yes. You can front the reason clause:

• Koska bussi on myöhässä, odotan junaa asemalla.

Both are correct. The first version (original) feels neutral; the second puts more focus on the reason first.

Finnish commonly expresses to be late with the phrase:

• olla myöhässä = to be late

Here myöhässä is the inessive form (-ssa/-ssä) and literally suggests being in a state of lateness. It’s an idiomatic, fixed-feeling expression.

On is the 3rd person singular present form of olla (to be):

• bussi on myöhässä = the bus is late

So on is just the normal present-tense copula is.

Finnish has no articles, so juna/junaa can be a train or the train. The intended meaning comes from context:

• If you’re at a station and there’s an expected train, odotan junaa will often be understood as I’m waiting for the (expected) train.
• If it’s more general, it can be a train.