Khi trời nắng và có gió, Lan vẫn mang áo khoác màu đen vì văn phòng rất lạnh.

Khi means when. It introduces a time clause:

• Khi trời nắng và có gió = When it is sunny and windy

In Vietnamese, this kind of clause can come before or after the main clause.

• Khi trời nắng và có gió, Lan vẫn mang áo khoác màu đen...
• Lan vẫn mang áo khoác màu đen khi trời nắng và có gió...

Both are grammatical. Putting the khi clause first sets the scene first, which is very common.

Vietnamese often does not need a verb like to be in weather expressions.

• trời nắng = it is sunny / sunny weather
• trời lạnh = it is cold
• trời mưa = it is raining / rainy

Here:

• trời = sky / weather
• nắng = sunlight / sunny

So trời nắng literally feels like the weather is sunny, but Vietnamese does not need a separate is.

Có gió literally means there is wind.

• có = have / there is / there are
• gió = wind

So:

• trời nắng và có gió = it is sunny and there is wind = it is sunny and windy

This is a very natural Vietnamese way to describe weather.

Vẫn means still, nevertheless, or even so, depending on context.

In this sentence, it shows contrast:

• Even though the weather is sunny and windy,
• Lan still brings/wears a black jacket.

So vẫn highlights that her action may seem surprising based on the weather.

Positionally, vẫn usually comes before the main verb:

• Lan vẫn mang...

Most basically, mang means bring, carry, or take along.

So mang áo khoác often means:

• bring a jacket
• carry a jacket

In this sentence, that makes good sense: the weather outside is sunny, but the office is cold, so Lan still brings a jacket.

If you specifically want to say wear a jacket, Vietnamese very often uses:

• mặc áo khoác

So a learner may notice that mặc áo khoác sounds more specifically like wearing a jacket, while mang áo khoác can suggest bringing it along. Context decides the best interpretation.

Both are possible, but they feel slightly different.

• áo khoác đen = a black jacket
• áo khoác màu đen = a jacket that is black in color

Màu đen is a bit more explicit because màu means color.

So:

• áo khoác đen is shorter and very common.
• áo khoác màu đen is also natural and may sound a little more descriptive or deliberate.

In Vietnamese, descriptive words usually come after the noun, not before it as in English.

So:

• áo khoác màu đen
  • áo khoác = jacket
  • màu đen = black color

This is a normal Vietnamese word order:

• noun + description

Other examples:

• xe đỏ = red car
• nhà lớn = big house
• áo trắng = white shirt

Vì means because.

It introduces the reason:

• vì văn phòng rất lạnh = because the office is very cold

So the structure is:

• situation: Khi trời nắng và có gió
• main action: Lan vẫn mang áo khoác màu đen
• reason: vì văn phòng rất lạnh

This is very similar to English logic.

Vietnamese does not use articles the same way English does. There is no direct equivalent of a/an/the in many ordinary sentences.

So:

• văn phòng can mean office, the office, or an office

The context tells you which is meant. In this sentence, English would most naturally translate it as the office, because it refers to the office relevant to Lan.

Both are possible, but they are used a little differently.

• rất lạnh = very cold
• lạnh lắm = very cold / so cold

Rất is a straightforward adverb meaning very.
Lắm is also an intensifier, but it often sounds a bit more expressive or conversational.

So:

• văn phòng rất lạnh is neutral and standard.
• văn phòng lạnh lắm is also natural, often a bit more spoken in tone.

The comma is natural and helpful here because the sentence begins with a time clause:

• Khi trời nắng và có gió, ...

It separates the background information from the main clause, just like in English:

• When it is sunny and windy, Lan still brings a black jacket...

In informal writing, punctuation in Vietnamese can sometimes be looser, but this comma is standard and clear.

Yes. Vietnamese allows some flexibility. For example:

• Lan vẫn mang áo khoác màu đen vì văn phòng rất lạnh khi trời nắng và có gió.
• Vì văn phòng rất lạnh, Lan vẫn mang áo khoác màu đen khi trời nắng và có gió.

But the original version is especially clear because it goes in a very logical order:

1. time/weather situation
2. main action
3. reason

That order is easy to follow.

Yes. Và means and, so it joins two conditions:

• trời nắng = it is sunny
• có gió = there is wind

Together:

• trời nắng và có gió = it is sunny and windy / sunny and there is wind

It means both are true in the same situation.

Not really. Lan is simply the subject of the sentence, like Lan or Anna in English.

Vietnamese often uses a person’s name directly where English might also use a pronoun in later sentences. So learners will often see names repeated more than in English.

Here:

• Lan vẫn mang áo khoác... = Lan still brings/wears a jacket...

Very straightforward.

A useful breakdown is:

• Khi + clause,
• subject + vẫn + verb + object,
• vì + reason clause

Applied here:

• Khi trời nắng và có gió = when it is sunny and windy
• Lan vẫn mang áo khoác màu đen = Lan still brings/wears a black jacket
• vì văn phòng rất lạnh = because the office is very cold

So the full pattern is:

• When X, Lan still does Y because Z.

This is a very useful structure you can reuse in your own Vietnamese sentences.