Jos viivästys jatkuu, lentoyhtiö antaa matkustajille uudet ohjeet.

Jos means if. It introduces a conditional subordinate clause: Jos viivästys jatkuu.

So the sentence has two parts:

• Jos viivästys jatkuu = the if clause
• lentoyhtiö antaa matkustajille uudet ohjeet = the main clause

Finnish uses jos very much like English if.

Finnish very often uses the present tense to talk about the future when the context makes the future meaning clear.

So:

• viivästys jatkuu literally looks like the delay continues
• lentoyhtiö antaa literally looks like the airline gives

But in this kind of sentence, the meaning is naturally future-oriented: If the delay continues, the airline will give...

Finnish does not have a separate future tense like English does, so present tense often does that job.

Because jatkua and jatkaa are different verbs.

• jatkua = to continue, to go on
• jatkaa = to continue something, to carry on something

Here, the delay is the thing that continues by itself, so Finnish uses the intransitive verb jatkua:

• viivästys jatkuu = the delay continues

If you used jatkaa, there would normally need to be someone continuing something:

• Lentoyhtiö jatkaa tiedottamista = The airline continues informing people

So jatkuu is the correct form here.

Viivästys is in the nominative singular, because it is the subject of the clause Jos viivästys jatkuu.

The thing doing the continuing is the delay, so it stays in its basic subject form:

• viivästys = a delay / the delay

Finnish subjects are very often in the nominative.

Finnish makes compound nouns very freely, and they are usually written as one word.

So:

• lento = flight
• yhtiö = company

Together:

• lentoyhtiö = airline

This is very normal in Finnish. English often uses two words where Finnish prefers one compound word.

Finnish does not have articles like English a, an, and the.

So words like:

• viivästys
• lentoyhtiö
• matkustajille
• uudet ohjeet

do not need any article. Whether English translates them as a delay, the delay, an airline, the airline, and so on depends on context.

That is completely normal in Finnish.

Because matkustajille is in the allative plural. Here it marks the recipient: the people who receive the instructions.

• matkustaja = passenger
• matkustajalle = to/for a passenger
• matkustajille = to/for passengers

With the verb antaa = to give, Finnish often marks the receiver with the allative:

• antaa matkustajille = give to the passengers / give passengers

So matkustajille tells you who gets the instructions.

This is about the Finnish object.

Here, uudet ohjeet is a total object in the plural. It suggests a complete set of instructions is being given.

• uudet ohjeet = the new instructions, as a complete whole

If you said uusia ohjeita, that would be the partitive plural, which sounds more like:

• some new instructions
• new instructions in an indefinite or incomplete sense

So the sentence uses uudet ohjeet because the airline is giving the passengers a definite set of replacement instructions.

In Finnish, adjectives usually agree with the noun they describe in number and often also in case.

So:

• uusi ohje = a new instruction
• uudet ohjeet = new instructions

Both words are plural here:

• uudet = new, plural
• ohjeet = instructions

This kind of agreement is very important in Finnish.

No. Jos does not automatically require the conditional mood.

In this sentence, both verbs are in the indicative present:

• jatkuu
• antaa

That is normal for a real or likely condition:

• Jos viivästys jatkuu, lentoyhtiö antaa matkustajille uudet ohjeet.

If you wanted to make it sound more hypothetical, Finnish could use the conditional:

• Jos viivästys jatkuisi, lentoyhtiö antaisi matkustajille uudet ohjeet.

So jos can appear with either, depending on the meaning. Here the plain present is the natural choice.

Because the sentence begins with a subordinate clause.

Finnish normally puts a comma between a subordinate clause and the main clause:

• Jos viivästys jatkuu, lentoyhtiö antaa matkustajille uudet ohjeet.

This is similar to English, where a comma is also often used when the if clause comes first.

Yes. Finnish word order is fairly flexible, although some orders sound more neutral than others.

This sentence is very natural as written:

• Jos viivästys jatkuu, lentoyhtiö antaa matkustajille uudet ohjeet.

But you could also put the jos clause later:

• Lentoyhtiö antaa matkustajille uudet ohjeet, jos viivästys jatkuu.

The basic meaning stays the same. The choice is mostly about emphasis and information flow. The original version is a very normal, neutral way to present the condition first.