Skolan slutar den nionde juni.

Because skolan is the definite form of skola.

• skola = a school
• skolan = the school

In Swedish, the definite article is often attached to the end of the noun instead of being a separate word like the in English.

So Skolan slutar ... means The school ends ..., or more naturally in English, School ends ...

Slutar is the present tense of sluta, which often means to end, to stop, or to finish.

In this sentence, Skolan slutar means that the school term, school year, or classes end on that date.

This is a common Swedish way to talk about school finishing for the term:

• Skolan slutar i juni.
• När slutar skolan?

Be careful: sluta can also mean quit in other contexts, such as:

• Jag ska sluta röka. = I’m going to quit smoking.

So the exact meaning depends on context.

Swedish often expresses dates with:

den + ordinal number + month

So:

• den nionde juni = the ninth of June / June ninth

Here:

• den = marks the date expression
• nionde = ninth
• juni = June

This is a very normal pattern in Swedish:

• den första maj = the first of May
• den tjugofjärde december = the twenty-fourth of December

Nionde is an ordinal number. It corresponds to English ninth.

Compare:

• nio = nine
• nionde = ninth

Swedish uses ordinal numbers for dates:

• första = first
• andra = second
• tredje = third
• fjärde = fourth
• nionde = ninth

So in dates, you normally do not use the basic number word nio. You use the ordinal nionde.

Because Swedish usually does not need a preposition here.

English says:

• on June ninth

But Swedish normally just says:

• den nionde juni

So the date expression works without a separate word meaning on.

This is very common with dates in Swedish.

Yes. That is also correct.

Swedish word order is flexible, and the date can be moved to the front for emphasis:

• Skolan slutar den nionde juni.
• Den nionde juni slutar skolan.

Both mean the same thing.

If you put the date first, Swedish still follows the verb-second rule, so slutar must come before skolan:

• Den nionde juni slutar skolan. ✅
• Den nionde juni skolan slutar. ❌

In this sentence, skolan usually means school as an activity or institution, not the physical building.

So Skolan slutar den nionde juni normally means:

• the school term ends
• classes finish
• students break up for summer

It usually does not mean that the building itself is somehow closing forever.

Context tells you that this is about the school schedule.

Because in Swedish, months are not capitalized.

So you write:

• juni
• maj
• december

This is different from English, where month names take a capital letter:

• June
• May
• December

The same is true for days of the week in Swedish:

• måndag
• tisdag

Yes, especially in writing.

You may see:

• Skolan slutar den 9 juni.
• Skolan slutar 9 juni.

But when speaking, people often say:

• den nionde juni or simply
• nionde juni

So the written and spoken forms do not always look exactly the same.

In a full spoken date with an ordinal, den is very common and standard:

• den nionde juni

In some contexts, especially less formal speech, people may say just:

• nionde juni

And in writing, a numeric date often appears without den:

• 9 juni

So:

• den nionde juni = very standard and complete
• nionde juni = also possible
• 9 juni = common in writing

A careful pronunciation would be roughly:

• den ≈ dehn
• nionde ≈ NEE-on-deh
• juni ≈ YOO-nee

A few helpful points:

• j in Swedish juni sounds like English y
• u in juni is not exactly the English oo, but yoo-nee is a useful approximation
• nionde has three clear parts: ni-on-de

In natural speech, den may sound a bit weaker and shorter than in very careful pronunciation.