sinsitu no mado wo akeru to kaze ga haitte, aratta siitu ga yoku kawakimasu.

の links two nouns. Here, 寝室の窓 means the bedroom window or more literally the window of the bedroom.

So:

• 寝室 = bedroom
• 窓 = window
• 寝室の窓 = bedroom window

This is one of the most common uses of の: showing possession, belonging, or a descriptive relationship between nouns.

Because 開ける is a transitive verb, meaning to open something. A transitive verb takes a direct object, and that object is marked by を.

So:

• 窓を開ける = open the window

If you wanted to say the window opens or the window is open/opened, you would use the intransitive verb 開く instead:

• 窓が開く = the window opens

This is a very common Japanese verb pair:

• 開ける = to open something
• 開く = something opens

Here, と means something like when or if, but with a strong sense of a natural or automatic result.

So 窓を開けると風が入って… means:

• When you open the window, wind comes in...
• or If you open the window, wind comes in...

This と is often used when one thing naturally leads to another:

• 春になると暖かくなる。
  When spring comes, it gets warm.

• このボタンを押すとドアが開きます。
  If you press this button, the door opens.

In your sentence, opening the window naturally causes the wind to come in.

入って is the て-form of 入る (to enter / to come in). Here it connects one action or event to the next.

The sentence structure is roughly:

• 窓を開けると風が入って、洗ったシーツがよく乾きます。

This means:

1. You open the window.
2. The wind comes in.
3. As a result, the washed sheets dry well.

The て-form often links clauses and can show sequence, cause, or a simple continuation of events. Here it connects wind comes in with the sheets dry well.

Because 入る is an intransitive verb. The wind is the thing that comes in, so it is marked as the subject with が.

• 風が入る = wind comes in

Japanese often uses が with intransitive verbs to mark the thing that undergoes the action or change.

Compare:

• 風を入れる = to let air/wind in
• 風が入る = wind comes in

Your sentence uses the intransitive pattern: the wind itself is entering.

洗った is the past/plain form of 洗う (to wash), and here it modifies the noun シーツ.

So:

• 洗ったシーツ = washed sheets / the sheets that were washed

This is a relative clause. Japanese puts the modifying clause before the noun:

• 洗った
  • シーツ
• literally: washed sheets

If you said 洗うシーツ, that would mean something more like the sheets that will be washed or the sheets one washes, which is not the intended meaning here.

Because Japanese relative clauses do not need a relative pronoun like that, which, or that were.

English:

• the sheets that I washed
• the washed sheets

Japanese:

• 洗ったシーツ

Japanese simply places the modifying clause directly before the noun. This is a major difference from English.

You can think of it as:

• [washed] sheets
• [I washed] sheets

The noun being modified comes at the end.

Because 乾く is intransitive: it means to dry in the sense that something becomes dry.

So:

• シーツが乾く = the sheets dry

The sheets are the subject of the change, so they take が.

If you wanted a transitive version, Japanese uses 乾かす:

• シーツを乾かす = dry the sheets

So the difference is:

• 乾く = to become dry
• 乾かす = to dry something

Here よく means well.

So:

• よく乾きます = dry well

It does not mean often in this sentence.

よく can mean different things depending on context:

• よく行きます = go often
• よく見えます = can see well
• よく乾きます = dries well

In this sentence, it describes the quality or effectiveness of the drying.

Japanese non-past forms often cover:

• present
• future
• habitual action
• general truth

Here, 乾きます is not necessarily talking about one single future event only. It expresses a general result:

• When you open the bedroom window, wind comes in, and the washed sheets dry well.

So it sounds like a general fact, tendency, or usual outcome.

The ます form is simply the polite style.

It can often suggest a general or predictable result, especially with と.

So this sentence sounds less like:

• I opened it once, and then...

and more like:

• Whenever you open the bedroom window, wind comes in, and the washed sheets dry well.

or

• If you open the bedroom window, wind comes in, and the washed sheets dry well.

The exact English translation depends on context, but the Japanese gives a strong sense of a natural consequence.

Because different clauses have different subjects.

Break it up like this:

• 寝室の窓を開けると = when the bedroom window is opened
• 風が入って = the wind comes in
• 洗ったシーツがよく乾きます = the washed sheets dry well

So:

• 風が marks wind as the subject of 入る
• シーツが marks sheets as the subject of 乾く

Japanese often has multiple small clauses in one sentence, and each clause can have its own subject.

It is omitted.

Japanese often leaves out subjects when they are understood from context. In 窓を開けると, the person opening the window is not explicitly stated.

Depending on context, it could mean:

• when I open the window
• when you open the window
• when one opens the window

In a general statement like this, English often translates it as when you open the window or if you open the window, even though Japanese does not actually say you.

The comma just helps readability. It shows a pause between linked parts of the sentence.

Japanese commas are often more flexible than English commas. Here it separates:

• 風が入って、
• 洗ったシーツがよく乾きます。

It is not marking a full stop or a major grammatical change; it just makes the sentence easier to read.

Yes. Japanese nouns usually do not change form for singular vs. plural.

So シーツ can mean:

• a sheet
• sheets

In this context, it is usually understood as sheets because that makes the most natural sense, but the noun itself does not have a special plural ending.

That is normal in Japanese:

• 本 = book / books
• 猫 = cat / cats
• シーツ = sheet / sheets