Learn Hardcore Finnish: Kuljettaja sanoo, että lentokentällä on ruuhkaa. - The driver says that there is a rush at the airport.

Että is a complementizer meaning that, introducing a subordinate clause: että lentokentällä on ruuhkaa. Finnish requires a comma before että (and many other subordinating conjunctions), so the comma is mandatory in standard writing: Kuljettaja sanoo, että …

What case is lentokentällä, and what does -llä mean?

Lentokentällä is in the adessive case (-lla/-llä), which often corresponds to English at/on with places. Here it means at the airport. The adessive is commonly used with locations like stations, stops, and open areas: asemalla (at the station), pysäkillä (at a bus stop), torilla (at the market square).

Could I say lentokentässä instead?

Lentokentässä (inessive, -ssa/-ssä = in/inside) would mean literally inside the airport/airfield area and is rarely used for traffic conditions. For everyday talk about what’s happening at that place, lentokentällä is the idiomatic choice. If you mean inside a specific building, you’d usually name it: terminaalissa (in the terminal).

What does on mean here?

On is the 3rd person singular present of olla (to be). In this existential construction it corresponds to English there is/are. So lentokentällä on ruuhkaa = there is congestion at the airport.

Why is ruuhkaa in that form and not just ruuhka?

Ruuhkaa is the partitive singular of ruuhka (congestion, traffic jam). In existential sentences (there is/are) Finnish uses the partitive for an indefinite or uncountable amount: on ruuhkaa ≈ there is (some) congestion. It emphasizes an unbounded amount rather than a single, delimited thing.

Can I ever say lentokentällä on ruuhka?

Possible but much less common. Ruuhka (nominative) would suggest a specific, delimited jam, e.g., a single, well-defined bottleneck. In general traffic reports and everyday speech, on ruuhkaa is the natural way to say there’s heavy traffic/congestion.

How would I say the airport is congested (using an adjective)?

Use the adjective ruuhkainen:

Lentokenttä on ruuhkainen. = The airport is congested. This describes a property of the airport, while lentokentällä on ruuhkaa reports the presence of congestion at that location.

Does Finnish mark the/the driver with articles?

Finnish has no articles. Kuljettaja can mean a driver or the driver depending on context. If you need to make it specific, context or demonstratives help: se kuljettaja (that/the driver just mentioned), tämä kuljettaja (this driver).

What tense is sanoo, and how would I say said?

Sanoo is present tense, 3rd person singular of sanoa (to say): he/she says. The past is sanoi: he/she said.

Kuljettaja sanoi, että … = The driver said that …

If I put the main verb in the past, does the että-clause also go to the past?

Not automatically. Finnish doesn’t enforce sequence-of-tenses like English often does. You choose the tense in the että-clause based on meaning:

Kuljettaja sanoi, että lentokentällä on ruuhkaa. (still true or generally true)
Kuljettaja sanoi, että lentokentällä oli ruuhkaa. (was true at that time)

Can että be dropped like English sometimes drops that?

In careful/standard Finnish, keep että. In casual speech it’s sometimes omitted, but writing and formal speech prefer the conjunction: Kuljettaja sanoo, että …

Why is the word order lentokentällä on ruuhkaa? Can I say on ruuhkaa lentokentällä?

The canonical existential pattern is: location (adverbial) + olla + indefinite noun phrase:

Lentokentällä on ruuhkaa. You can move elements for focus/contrast:
Ruuhkaa on lentokentällä (emphasizes where the congestion is).
On ruuhkaa lentokentällä is possible but marked; the neutral, most common form puts the location first.

What exactly does kuljettaja mean? Is there a more colloquial option?

Kuljettaja is the neutral/polite word for driver. A common informal synonym is kuski (can sound casual or slangy). For specific jobs you can specify: bussinkuljettaja (bus driver), taksinkuljettaja (taxi driver).

Could I express the message with direct speech instead of an että-clause?

Yes. For direct quotation you can use a colon and then the speech:

Kuljettaja sanoo: Lentokentällä on ruuhkaa. In writing, punctuation/formatting varies, but this shows the difference between reported speech (että) and direct speech.

How do I pronounce the special letters here?

ä: a front vowel, like the a in English cat (but longer/clearer in Finnish).
j: like English y in yes (so kuljettaja sounds roughly like kul-yet-ta-ya).
Double letters matter: tt is a long t; aa in ruuhkaa is a long a. Length changes meaning in Finnish.