samui asa ha yakan de oyu wo wakasite, otya wo nomimasu.

Because 寒い is an い-adjective, and い-adjectives can modify nouns directly.

• 寒い朝 = a cold morning

You only need な with な-adjectives, such as:

• 静かな朝 = a quiet morning

So 寒い朝 is the normal and correct form.

Here, は marks 寒い朝 as the topic.

So 寒い朝は has the sense of:

• as for cold mornings
• on cold mornings
• when it’s a cold morning

It sets the situation for the rest of the sentence. The speaker is talking about what they do in that kind of situation.

は and に do different jobs.

• 寒い朝は = on cold mornings / as for cold mornings
  This sounds like a general habit or repeated action.

• 寒い朝に = on a cold morning
  This more often points to a specific time when something happens.

Because this sentence describes something the speaker عادة does, は is the more natural choice.

Yes, the subject is omitted, which is very common in Japanese.

From context, it is most naturally understood as:

• I boil water and drink tea
• or sometimes we / people in a broader context

Japanese often leaves out subjects when they are obvious from the situation.

Here, で marks the means / tool / vessel used for the action.

So やかんで means:

• using a kettle
• in a kettle

It is not mainly about location here. It tells you what is used to boil the water.

Yes, お湯 does mean hot water, so this can feel strange to English speakers at first.

But in Japanese, お湯を沸かす is a very common expression. It means:

• to heat/boil water to make hot water
• to boil water

Japanese often focuses on the resulting hot water, not just the starting cold water.

You can also hear 水を沸かす, but お湯を沸かす is very natural in everyday speech.

This is a transitive / intransitive pair.

• 沸く = to boil / to come to a boil
  The water itself boils.

• 沸かす = to boil something / to make something boil
  Someone causes the water to boil.

In this sentence, the speaker is actively boiling the water, so 沸かす is correct.

• お湯が沸く = the water boils
• お湯を沸かす = boil the water

The て-form connects actions.

Here it means the actions happen in sequence:

1. boil the water
2. drink tea

So 沸かして、お茶を飲みます means something like:

• I boil water and drink tea
• I boil water, then drink tea

In this sentence, the connection is mainly a simple sequence of actions.

Japanese non-past forms can refer to the present, the future, or habitual actions depending on context.

Here, because of 寒い朝は, the sentence is understood as a habitual action:

• On cold mornings, I drink tea

So 飲みます here is not really a one-time future. It describes what the speaker usually does.

The お is a polite prefix. It often makes words sound more natural, soft, or refined in everyday Japanese.

With these words, the prefix is extremely common:

• お湯 = hot water
• お茶 = tea

These are not especially formal here; they are just the normal everyday forms people often use.

It depends on context.

In everyday Japanese, お茶 often refers to Japanese green tea, especially if nothing else is specified. But it can also mean tea more generally.

If someone wants to be specific, they might say:

• 緑茶 = green tea
• 紅茶 = black tea
• 麦茶 = barley tea

So in this sentence, お茶 most naturally suggests ordinary tea in a Japanese setting, often green tea.

Japanese often leaves out steps that are easy to guess from context.

If someone says:

• やかんでお湯を沸かして、お茶を飲みます

the listener naturally understands that the speaker boils water, prepares the tea, and then drinks it. The middle step does not have to be stated if it is obvious.

This kind of omission is very common in Japanese.