När solen skiner sitter vi gärna på balkongen.

Because Swedish uses V2 word order in main clauses: the finite verb has to come in the second position.

Here, När solen skiner is an introductory subordinate clause occupying the first position. That means the main clause must start with the verb:

• När solen skiner sitter vi gärna på balkongen.

If you started directly with the main clause, you would say:

• Vi sitter gärna på balkongen när solen skiner.

So the change in word order happens because the sentence begins with När solen skiner.

Gärna is a very common Swedish adverb. It often means something like:

• gladly
• with pleasure
• like to
• quite happily

In this sentence, it gives the idea that we like to sit on the balcony or we happily sit on the balcony when the sun is shining.

So vi sitter gärna på balkongen is not just a neutral we sit on the balcony, but more like:

• we like sitting on the balcony
• we’re happy to sit on the balcony
• we tend to sit on the balcony

Because solen is the definite form of sol:

• en sol = a sun
• solen = the sun

Swedish usually attaches the definite ending to the noun itself, instead of using a separate word like the.

So:

• sol = sun
• solen = the sun

That is why the sentence says När solen skiner = When the sun is shining.

Skiner is the present tense of the verb skina, which means to shine.

So:

• skina = to shine
• skiner = shines / is shining

In Swedish, the same present-tense verb form is used for all persons:

• jag skiner
• du skiner
• han/hon skiner
• vi skiner

Unlike English, Swedish does not add a special -s only for he/she/it.

Yes, sitter literally means sit / are sitting, from the verb sitta.

But Swedish often uses posture verbs more naturally than English does. Where English might say:

• we are on the balcony
• we spend time on the balcony

Swedish often says:

• vi sitter på balkongen

This usually suggests that people are physically sitting there, but in many everyday contexts it can also simply mean that they are spending time there in a seated, relaxed way.

So in this sentence, sitter is both literal and very natural.

Because in Swedish you are normally on a balcony, not in it.

So:

• på balkongen = on the balcony

This matches English quite closely here. I balkongen would sound wrong in normal usage, because a balcony is thought of as a platform or surface you are on, not an enclosed space you are inside.

Yes. När here means when and introduces a subordinate clause:

• När solen skiner = When the sun is shining

It connects the time clause to the main clause.

So the structure is:

• När solen skiner = subordinate time clause
• sitter vi gärna på balkongen = main clause

This is a very common Swedish pattern.

In this sentence, gärna comes after the finite verb in the main clause:

• sitter vi gärna på balkongen

That is a very typical placement for sentence adverbs and similar adverbs in Swedish main clauses.

Compare:

• Vi sitter gärna på balkongen.
• När solen skiner sitter vi gärna på balkongen.

So even though the word order changes because of V2, gärna still stays after the finite verb sitter.

Yes, absolutely.

That version is also correct:

• Vi sitter gärna på balkongen när solen skiner.

The meaning is basically the same. The difference is mainly focus and style:

• När solen skiner sitter vi gärna på balkongen.
  This starts by emphasizing the time condition: when the sun shines...
• Vi sitter gärna på balkongen när solen skiner.
  This starts with we, so it feels a bit more straightforward.

Both are natural.

In Swedish, a comma after an introductory subordinate clause is often optional, and in short, simple sentences it is very often left out.

So:

• När solen skiner sitter vi gärna på balkongen.

is completely normal.

You may sometimes see:

• När solen skiner, sitter vi gärna på balkongen.

but the version without the comma is usually more standard in everyday Swedish for a short sentence like this.

Yes. Swedish present tense often covers both meanings that English separates into:

• shines
• is shining

So När solen skiner can mean:

• When the sun shines
• When the sun is shining

Which English version sounds best depends on context, but the Swedish form stays the same.

Yes.

• en balkong = a balcony
• balkongen = the balcony

Just like solen, the noun gets a definite ending:

• sol → solen
• balkong → balkongen

So på balkongen means on the balcony, not just on a balcony.