tā shàng wǎngkè de shíhou zǒngshì dài zhe ěrjī, suǒyǐ pángbiān de rén tīngbujiàn lǎoshī de shēngyīn.

In Mandarin, 上课 literally uses 上, but the meaning is to attend class / have class. So:

• 上课 = to attend class
• 上网课 = to take online classes

This is just a standard verb-object expression. 上 has many meanings in Chinese, and here it does not mean up. It means something more like to participate in or to engage in a class.

Examples:

• 我上午上课。 = I have class in the morning.
• 她在家上网课。 = She takes online classes at home.

的时候 means when or at the time when.

The pattern is:

[verb phrase] + 的时候

So here:

• 上网课 = attending online class
• 上网课的时候 = when attending online class / when she is taking online classes

The 的 links the action phrase to 时候.

More examples:

• 吃饭的时候不要看手机。 = Don’t look at your phone when eating.
• 下雨的时候我不想出门。 = When it rains, I don’t want to go out.

You can think of 上网课的时候 as a time expression placed before the main action.

Actually, in the full sentence, it is 她上网课的时候.

The structure is:

• 她 = she
• 上网课的时候 = when she is taking online classes
• 总是戴着耳机 = always wears headphones

Chinese often puts the subject first, and then the time phrase follows it:

她上网课的时候，总是戴着耳机。

This is very natural. You could also sometimes repeat subjects in longer sentences, but here it is unnecessary because 她 already clearly applies to the first clause.

总是 means always.

It usually comes before the verb phrase it modifies:

• 她总是戴着耳机。 = She always wears headphones.

In this sentence, it comes after the time phrase:

• 她上网课的时候，总是戴着耳机。

That means: When she takes online classes, she always wears headphones.

This placement is very common:

[subject] + [time phrase] + 总是 + [verb phrase]

Examples:

• 我早上总是喝咖啡。 = I always drink coffee in the morning.
• 他考试前总是很紧张。 = He is always nervous before exams.

着 shows a continuing state.

• 戴耳机 can mean wear headphones in a general sense
• 戴着耳机 emphasizes that the headphones are on / being worn

So in this sentence, 戴着耳机 describes her ongoing state while she is in class.

Compare:

• 她戴耳机。 = She wears headphones. / She puts on headphones. (more general)
• 她戴着耳机。 = She is wearing headphones. / She has headphones on.

This use of 着 is common with clothing and accessories:

• 穿着外套 = wearing a coat
• 戴着帽子 = wearing a hat
• 开着门 = the door is open

Not exactly.

English -ing often describes an ongoing action, but 着 often describes an ongoing state resulting from an action.

So:

• 戴着耳机 is closer to having headphones on or wearing headphones
• not exactly putting on headphones

A useful contrast:

• 她在戴耳机。 = She is putting on headphones / in the process of wearing them
• 她戴着耳机。 = She is wearing headphones

So 着 does not simply equal English -ing. It often marks a sustained condition.

旁边的人 literally means the person/people at the side or the people nearby.

Breakdown:

• 旁边 = beside / nearby / next to
• 的 = links a modifier to a noun
• 人 = person / people

So 旁边的人 means the people nearby or the person next to her, depending on context.

In Chinese, modifiers usually come before the noun:

• 中国人 = Chinese person
• 漂亮的衣服 = beautiful clothes
• 旁边的人 = the person/people nearby

Even though 人 is singular in form, Chinese nouns usually do not change form for singular/plural, so context decides whether it means person or people.

听不见 is a very common Chinese pattern:

verb + 不 + complement

Here:

• 听 = listen / hear
• 见 = perceive / catch with the senses
• 听见 = hear
• 听不见 = cannot hear

This is called a result complement or, in this negative form, often discussed as a potential complement. It shows whether the action reaches a result.

So:

• 听见 = manage to hear / hear
• 听不见 = cannot hear

Other similar examples:

• 看见 = see
• 看不见 = cannot see
• 找到了 = found it
• 找不到 = can’t find it

Both can often be translated as can’t hear, and in many everyday situations they overlap.

A rough distinction:

• 听不见 focuses on not perceiving the sound
• 听不到 often focuses on the sound not reaching you or being beyond your ability to hear

In many real sentences, either may sound natural.

Examples:

• 我听不见你说什么。 = I can’t hear what you’re saying.
• 这里太远了，听不到。 = It’s too far away to hear.

In your sentence, 听不见老师的声音 is very natural because it emphasizes that the nearby people are unable to perceive the teacher’s voice.

老师的声音 means the teacher’s voice or the voice of the teacher.

The particle 的 marks possession or association:

• 老师 = teacher
• 声音 = voice / sound
• 老师的声音 = the teacher’s voice

In Chinese, this is the normal way to connect a noun to another noun when the first one possesses or describes the second.

Examples:

• 我的书 = my book
• 他的名字 = his name
• 妈妈的手机 = mom’s phone

Sometimes 的 can be omitted in certain close relationships or set expressions, but here 老师的声音 is the standard and natural form.

声音 is a broad word meaning sound or voice, depending on context.

So:

• 老师的声音 = the teacher’s voice
• 奇怪的声音 = a strange sound
• 外面的声音很大。 = The sound outside is loud.

Chinese often uses one word where English may choose different words depending on context. Here, because the source is 老师, English naturally says the teacher’s voice.

所以 means so or therefore.

It introduces the result of the earlier situation:

• She always wears headphones during online classes,
• so the people nearby can’t hear the teacher’s voice.

This is a very common pattern:

A，所以B = A, so B

Examples:

• 下雨了，所以我不出门。 = It’s raining, so I’m not going out.
• 他很忙，所以没来。 = He was busy, so he didn’t come.

In speech, Chinese speakers sometimes omit 所以 if the relationship is already clear, but including it makes the cause-result connection explicit.

It can be either, depending on context.

Chinese nouns usually do not change form for singular vs. plural the way English nouns do. So:

• 旁边的人 can mean the person nearby
• or the people nearby

In this sentence, English might naturally translate it as the people nearby because that sounds more general, but the person next to her could also fit in the right context.

If Chinese wants to make plurality clearer, it might say:

• 旁边的人们 = the people nearby

But 人们 is not always used in ordinary conversation, and 旁边的人 is perfectly normal.

Yes. 时 is a shorter, more formal version of 时候 in many contexts.

So you could say:

她上网课时总是戴着耳机。

This means the same thing: When she takes online classes, she always wears headphones.

Difference in tone:

• 的时候 = more common in everyday speech
• 时 = shorter, often a bit more written or formal

Both are correct here.

Chinese often builds the sentence in this order:

subject + time/situation + adverb + verb phrase + result

Here that gives:

• 她 = subject
• 上网课的时候 = time/situation
• 总是 = adverb
• 戴着耳机 = verb phrase
• 所以旁边的人听不见老师的声音 = result

English often uses a similar order, but Chinese is especially comfortable putting time information early in the sentence.

A good habit for learners is to look for this pattern:

• who
• when / under what circumstances
• how often / attitude
• what action
• what result

That will make long Chinese sentences much easier to understand.