madogawa no seki ga aitara, osiete kudasai.

窓側 literally means the window side.

In this sentence, 窓側の席 means a seat on the window side or simply a window seat.

A useful breakdown is:

• 窓 = window
• 側 = side

So 窓側 is a noun meaning the side near the window.

The の connects two nouns.

• 窓側 = window side
• 席 = seat

So 窓側の席 means the seat of the window side, which in natural English becomes the window seat or a seat by the window.

This is a very common Japanese pattern:

• 駅の近く = the area near the station
• 日本の文化 = Japanese culture
• 窓側の席 = a window-side seat

が marks 席 as the thing that becomes available.

In 席が空いたら:

• 席 = seat
• が = subject marker
• 空いたら = if/when it opens up / becomes vacant

So the seat is the thing undergoing the change.

Why not the others?

• を would be wrong here because 空く is intransitive. The seat does not get acted on by something else; it itself becomes empty.
• は is possible in some contexts, but it would sound more like you are setting the seat up as the topic. が is the natural choice when focusing on the seat becoming available.

It comes from the verb 空く（あく）, which means things like:

• to become empty
• to become available
• to open up (in the sense of space or availability)

For seats, rooms, tables, schedules, etc., 空く is very common.

Examples:

• 席が空く = a seat becomes available
• 部屋が空く = a room becomes vacant
• 時間が空く = time opens up / one becomes free

So 空いたら means if/when it becomes available.

〜たら is a very common way to say if or when.

Here, 席が空いたら means:

• if a window seat becomes available
• when a window seat opens up

Why たら works well here:

• It sounds natural for a specific future condition.
• It often has the nuance once that happens, then...

Compared with others:

• 空くと can sound more like a general rule: when it opens, ...
• 空けば is also grammatical, but 〜たら often feels a bit more conversational and direct in requests like this

So 空いたら、教えてください is a very natural everyday way to say it.

It can feel like either, depending on context.

Here it is something like:

• If a window seat becomes available, please let me know
• When a window seat becomes available, please let me know

In English, both are possible. Japanese 〜たら often leaves that slightly open.

The basic idea is: once that condition happens, please do this.

Because with seats, tables, rooms, and similar things, 空く often refers to availability, not just physical emptiness.

For example:

• A restaurant table may be occupied now.
• When the customers leave, the table 空く.
• That means it is now open / vacant / available.

So 席が空いたら is not just describing an empty seat in an abstract way. It means when that seat opens up for use.

Not in this sentence.

Although 教える often means to teach, it can also mean to tell or to inform someone.

So 教えてください here means:

• please tell me
• please let me know

That is very common in Japanese.

Examples:

• 名前を教えてください。 = Please tell me your name.
• 時間を教えてください。 = Please tell me the time.

So in this sentence, it definitely means please let me know.

〜てください is a standard polite way to make a request.

So:

• 教えて = te-form of 教える
• ください = please give / please do

Together, 教えてください means please tell me.

It is polite and normal in many situations, such as speaking to staff.

Other request forms exist, but they have different tones:

• 教えて = casual
• 教えてもらえますか = softer, a bit more indirect
• 教えていただけますか = more formal/polite

So 教えてください is straightforward and polite.

The subject is omitted, which is very normal in Japanese.

The implied meaning is:

• (You / staff member), please let me know

Japanese often leaves out subjects when they are obvious from context.

So the sentence does not need to say あなたが or 店員さんが. That would usually sound unnecessary.

Yes. Japanese often leaves that out too.

教えてください here really means:

• Please tell me
• Please let me know

The me is understood from context, even though it is not stated.

If you wanted to say it explicitly, you could say something like:

• 空いたら、私に教えてください。

But in normal conversation, that is usually unnecessary.

It is polite, but not extremely formal.

Why:

• 空いたら is neutral/plain inside the condition
• 教えてください is a polite request

This is very normal Japanese for speaking to staff in a restaurant, train, airplane, waiting area, etc.

If you wanted to sound even more formal, you could say:

• 窓側の席が空きましたら、教えてください。
• 窓側の席が空いたら、知らせていただけますか。

But the original sentence is already polite and natural.

Both can be understood, but they are slightly different.

• 窓側 = the window side
• 窓際 = right by the window / at the window

For seating, 窓側の席 is very natural when contrasting it with aisle side or inner side seating. It emphasizes which side the seat is on.

窓際の席 often emphasizes being right next to the window.

In many situations, both are fine, but 窓側の席 fits very naturally when asking for a window-side seat.

Yes, that is a very helpful way to see it.

The pattern is:

• Aたら = if/when A happens
• Bしてください = please do B

So here:

• 窓側の席が空いたら = if/when a window seat becomes available
• 教えてください = please let me know

This is a very common sentence pattern in Japanese.

Examples:

• 着いたら、電話してください。 = When you arrive, please call me.
• 分からなかったら、聞いてください。 = If you do not understand, please ask.

Yes. It can be used anywhere a window-side seat might become available.

For example:

• on a train
• on an airplane
• in a waiting area
• in a café
• in a classroom or event space

The sentence is general enough to work in many situations where seats may open up.