fuyu wa futon ni hairu mae ni, makura no chikaku ni hon o oite oku.

冬は sets winter as the topic or time frame: as for winter / in winter.

It does not mean winter is the subject doing something. It just tells you the sentence is talking about what happens in winter.

• 冬は = in winter / as for winter
• Compare:
  • 冬に can also mean in winter, but 冬は often feels more like speaking generally about winter or contrasting winter with other seasons.

So here, 冬は suggests something like:

• In winter, I put a book near my pillow before getting into bed.

Japanese often leaves out the subject when it is obvious from context.

In this sentence, there is no explicit I, you, or someone. The natural assumption is usually:

• I
• or the person being talked about, if context already established that

So this sentence could naturally mean:

• In winter, I put a book near my pillow before getting into the futon.

Japanese does this all the time, and it sounds very natural.

The particle に marks the place you enter into.

• 布団に入る = to get into the futon
• 家に入る = to enter the house
• お風呂に入る = to get into the bath / take a bath

With 入る, に often marks the destination or the place you end up in.

So:

• 布団に入る前に = before getting into the futon

布団 usually means a Japanese-style futon, the bedding you sleep in, often laid out on the floor.

It is not exactly the same as ベッド, which means a Western-style bed.

In English, depending on context, 布団に入る is often translated naturally as:

• get into bed
• get under the covers
• get into the futon

So the literal image is getting into the bedding, not climbing onto a bed frame.

前に means before.

When you put a verb before 前に, you use the dictionary form of the verb:

• 食べる前に = before eating
• 寝る前に = before sleeping
• 布団に入る前に = before getting into the futon

So the pattern is:

• Verb (dictionary form) + 前に

This is an important grammar pattern.

They do different jobs.

1. 布団に入る

   • に marks the place entered
   • into the futon

2. 枕の近くに本を置いておく

   • に marks the place where the book is placed
   • near the pillow

So even though both are に, they are attached to different parts of the sentence and have different roles.

枕 = pillow
近く = nearby area / vicinity
枕の近く = the area near the pillow
枕の近くに = near the pillow

The の connects the noun and the location expression:

• 駅の近く = near the station
• 家の近く = near my house
• 枕の近く = near the pillow

Then に marks that as the place where the book is put.

This is one of the most important points in the sentence.

• 置く = to put / place
• 置いておく = to put and leave there, often in advance or for later convenience

So 置いておく often implies preparation.

Here, the nuance is:

• Before getting into the futon, I place a book near the pillow ahead of time so it will be there later.

That extra sense of preparing beforehand is why 置いておく is used.

〜ておく usually has one of these meanings:

1. Do something in advance

   • 予約しておく = make a reservation in advance
   • 読んでおく = read beforehand

2. Do something and leave it that way

   • 窓を開けておく = leave the window open
   • 本を置いておく = leave a book there

In this sentence, both ideas fit:

• the book is placed beforehand
• and it is left there near the pillow

It can be, but in modern Japanese, the auxiliary おく in 〜ておく is very often written in hiragana:

• 置いておく ← most common
• 置いて置く ← possible, but usually less natural-looking in ordinary writing

Why?

Because the first 置いて is the main verb to place, while the second おく is an auxiliary expression meaning do in advance / leave as is. Auxiliary words are often written in hiragana.

Because 本 is the direct object of 置く.

• 本を置く = put a book
• 本を置いておく = put a book and leave it there / put a book in advance

The thing being placed is the book, so it takes を.

Not necessarily every single day, but it sounds like a habit, custom, or general practice in winter.

So the nuance is something like:

• In winter, I make a habit of putting a book near my pillow before getting into bed.

Japanese often uses the non-past form like this to describe repeated or habitual actions.

Yes, literally it is enter the futon, and yes, it is very common.

In English, that sounds a little unusual if translated word-for-word, but in Japanese it is a normal everyday expression.

Common similar expressions:

• 布団に入る = get into the futon / get into bed
• ベッドに入る = get into bed
• 布団から出る = get out of the futon

So you should understand it as a natural sleeping-related expression, not as strange or overly literal Japanese.

The comma separates the time/setup part from the main action.

• 冬は布団に入る前に、
  • In winter, before getting into the futon,
• 枕の近くに本を置いておく。
  • I place a book near the pillow in advance.

It makes the sentence easier to read. Japanese commas are often used more flexibly than English commas, but here it helps show the pause after the introductory phrase.

Yes, depending on context, that can be a natural English translation.

Literally:

• before getting into the futon

More natural in some English contexts:

• before going to bed

But there is a slight difference:

• 布団に入る前に specifically refers to the moment before physically getting into the futon
• before going to bed can be a little broader

So if you want the most literal meaning, keep getting into the futon. If you want smoother English, before going to bed may work well.