När solen skiner ser jag damm på bordet, så jag måste damma igen.

In Swedish, the definite article is usually attached to the end of the noun.

• sol = sun

• solen = the sun

• bord = table
• bordet = the table

The ending depends on the noun’s gender:

• en-words usually take -en in the definite singular
• ett-words usually take -et in the definite singular

So:

• en sol → solen
• ett bord → bordet

That is why Swedish says solen and bordet where English uses the sun and the table.

Here, när means when.

It is used for something that happens regularly, generally, or whenever a situation occurs:

• När solen skiner ... = When the sun shines ...

You would not normally use om here, because om usually means if, not when.

So:

• När solen skiner = when the sun shines / whenever the sun shines
• Om solen skiner = if the sun shines

In this sentence, the speaker means that every time the sun shines, they notice the dust, so när is the natural choice.

Skina is the infinitive, meaning to shine.
Skiner is the present tense, meaning shines or is shining.

So:

• skina = to shine
• skiner = shines

In the clause När solen skiner, you need a finite verb, because it is a complete clause with a subject and verb:

• subject: solen
• verb: skiner

That is why skiner is correct.

This is because of Swedish word order.

The sentence begins with a subordinate clause:

• När solen skiner

After that, the main clause follows:

• ser jag damm på bordet

In Swedish main clauses, the finite verb normally comes in the second position. This is often called V2 word order.

So when another element comes first, the verb must come before the subject:

• Jag ser damm på bordet.
• När solen skiner ser jag damm på bordet.

Not:

• När solen skiner jag ser damm på bordet ❌

This inversion is very important in Swedish.

Because they are related words:

• damm = dust
• damma = to dust

So in the sentence:

• ser jag damm på bordet = I see dust on the table
• jag måste damma igen = I have to dust again

This kind of noun/verb pair is common in Swedish. The verb is formed from the noun, and here it means remove dust / do the dusting.

Because måste is a modal verb, and modal verbs in Swedish are followed directly by the infinitive without att.

So:

• jag måste damma = I must dust / I have to dust

Not:

• jag måste att damma ❌

Other modal verbs work the same way:

• jag kan simma = I can swim
• jag vill läsa = I want to read
• jag ska gå = I will go / I’m going to go

So måste damma is exactly the normal pattern.

Igen means again.

So jag måste damma igen means:

• I have to dust again

It implies that the speaker has dusted before, but now needs to do it one more time.

In Swedish, igen often comes near the end of the clause:

• Jag måste damma igen
• Han kom igen
• Kan du säga det igen?

På usually means on.

So:

• damm på bordet = dust on the table

That is the natural preposition here because the dust is located on the surface of the table.

If you are talking about removing dust, Swedish often uses damma with a direct object:

• damma bordet = dust the table

But in this sentence, the first part is about where the dust is:

• ser jag damm på bordet = I see dust on the table

Så here means so.

It connects the first idea to the result:

• När solen skiner ser jag damm på bordet = When the sun shines, I see dust on the table
• så jag måste damma igen = so I have to dust again

It shows consequence: because the speaker can see the dust, they need to dust again.

The comma after bordet is natural and helpful here because the sentence is fairly long and has two parts:

• När solen skiner ser jag damm på bordet, så jag måste damma igen.

In modern Swedish, commas are often lighter and less strict than in some forms of English. A short sentence may sometimes be written without a comma, but here the comma makes the structure clearer.

So it is a good, natural choice in this sentence.

Yes. In this sentence, it most naturally has a general meaning:

• Whenever the sun shines, I see dust on the table

That is because the whole sentence sounds like a repeated experience, not one single event. The sunlight makes the dust visible, and this seems to happen again and again.

So när can refer to:

• a specific time: when
• a repeated situation: whenever

Here, the repeated meaning fits very well.