samui hi ha atui kooto wo kite dekakemasu.

は marks 寒い日 as the topic: as for cold days or on cold days.

So 寒い日は does not mean just the cold day. It sets up a general situation:

• On cold days, ...
• When it’s a cold day, ...

This is a very common Japanese pattern:

• 忙しい日は、家で食べます。
• 休みの日は、よく寝ます。

You may also see 寒い日には, which adds に and makes the time/condition feel a little more explicitly marked.

Because 寒い is an い-adjective.

い-adjectives directly modify nouns:

• 寒い日 = cold day
• 厚いコート = thick coat
• 新しい本 = new book

Only な-adjectives use な before a noun:

• 静かな部屋
• 便利な店

So 寒い日 is the correct form.

Here, 日 is read ひ.

So:

• 寒い日 = さむいひ

This is a common reading when 日 means day in an everyday sense.

Compare:

• 一日 = いちにち or ついたち depending on meaning
• 日曜日 = にちようび

Kanji readings often depend on the whole word, not just the individual kanji by itself.

を marks コート as the direct object of 着る.

So:

• コートを着る = to wear/put on a coat

In this sentence, the thing being worn is 厚いコート, so it takes を.

A few examples:

• 帽子をかぶります。
• 靴をはきます。
• シャツを着ます。

着て is the て-form of 着ます. The て-form is used to connect actions.

So:

• コートを着て、出かけます = put on a coat and go out

Japanese often links actions this way:

• 朝ご飯を食べて、学校へ行きます。
• ドアを開けて、外に出ます。

If you said 着ます。出かけます。, that would sound like two separate sentences. 着て smoothly connects them into one action sequence.

Usually it suggests both.

The basic sequence is:

1. put on the coat
2. go out

But because putting on clothes creates a continuing state, it also naturally implies:

• go out wearing the coat

So in normal usage, 厚いコートを着て出かけます means you go out with the coat on.

出かけます means go out, head out, or leave home/base and go somewhere.

It focuses on the idea of going out from where you are.

行きます simply means go and often focuses more on movement to a destination.

So:

• 出かけます = go out / head out
• 行きます = go

In this sentence, 出かけます fits well because the idea is about getting dressed appropriately before going out.

By itself, it sounds general or habitual.

So it means something like:

• On cold days, I go out wearing a thick coat.
• When it’s cold, I wear a thick coat before going out.

There is no clear marker for one particular day here.

If you wanted a specific day, you would usually make that clearer with context or wording like:

• その寒い日は...
• 昨日は寒かったので...

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

So even though English usually says I, Japanese often just says:

• 寒い日は厚いコートを着て出かけます。

The listener will usually understand the subject as:

• I
• we
• or a general person, depending on context

If you want to make it explicit, you can say:

• 私は寒い日は厚いコートを着て出かけます。

But in many situations, that is unnecessary.

Yes, 厚い literally means thick.

In Japanese, describing a coat as thick is very natural, because a thick coat is understood to give more warmth. So:

• 厚いコート = a thick coat

If you want to emphasize warmth rather than thickness, you could also say:

• 暖かいコート = a warm coat

The nuance is slightly different:

• 厚いコート focuses on physical thickness
• 暖かいコート focuses on how warm it is

Both are natural, depending on what you want to emphasize.

Because Japanese is basically a verb-final language.

A very common Japanese sentence pattern is:

• time/topic + object + verb

So here:

• 寒い日は = on cold days
• 厚いコートを = a thick coat
• 着て出かけます = put on and go out

This can feel backwards to English speakers at first, but it is completely normal in Japanese. Modifiers and details usually come before the main verb, and the verb finishes the sentence.