Learn Hardcore Chinese: Zài huǒchēzhàn gēn péngyou shuō zàijiàn de shíhou, tā xiān kū le yíhuìr, hòulái yòu xiào le. - When saying goodbye to her friend at the train station, she first cried for a while and then smiled again.

Chinese often puts a time / situation phrase at the beginning to set the scene.
在火车站跟朋友说再见的时候 is a time‑clause meaning “when (she was) saying goodbye to her friend at the train station”.
So the structure is:

在火车站跟朋友说再见的时候，她…
= When (she) was saying goodbye at the station, she…

You could also say:

她在火车站跟朋友说再见的时候，先哭了…

Both are grammatical. Putting the time/situation clause first is just very natural in Chinese narrative.

What exactly does 在 do in 在火车站? Is it required?

在 is a preposition meaning “at / in / on”.
在火车站 literally means “at the train station”.

Without 在, 火车站跟朋友说再见的时候 sounds incomplete or odd, because Chinese normally marks locations with 在.
There are other ways to express location (e.g. just 火车站上 in some contexts), but for a straightforward “at the train station”, 在火车站 is the normal, basic form.

What does 跟 mean in 跟朋友说再见? Can I use 和 instead?

Here 跟 means “with”, indicating the person you’re interacting with:

跟朋友说再见 = “say goodbye to / with a friend”.

You can usually replace 跟 with 和 in this kind of sentence:

在火车站和朋友说再见的时候…

Both are fine; 和 is slightly more neutral and formal, 跟 is very common in speech. In beginner contexts they are often interchangeable.

Why is it 跟朋友说再见 and not 对朋友说再见?

Both are possible, but there’s a nuance:

跟朋友说再见 focuses on an interaction with someone (“say goodbye with your friend / together”).
对朋友说再见 focuses more on direction (“say goodbye to your friend”).

In everyday speech, 跟…说再见 is more common and feels more natural here. 对…说再见 is grammatical but a bit less idiomatic in this particular sentence.

What is the function of 的时候 here? Why do we need 的 before 时候?

时候 means “time, moment”.
When you put a verb phrase in front of it, you usually add 的 to turn that whole phrase into a noun-like phrase:

在火车站跟朋友说再见的时候
= “the time of (her) saying goodbye to her friend at the train station”
= “when she was saying goodbye…”

The 的 is almost always used when the part before 时候 is a longer phrase or a complete action/event.
Very short expressions like 小时候 (“when (I was) little”) often drop 的, but here 的 is needed.

What does 先 do in 她先哭了一会儿?

先 means “first / first of all / earlier in sequence”.
It shows that crying is the first action in a series:

她先哭了一会儿 = “She first cried for a while”
Followed by 后来又笑了 = “then later (she) laughed”

Common patterns:

先 A，再 B (first A, then B)
先 A，然后 B
Here: 先 A，后来 B – same idea of ordering events.

What is the difference between 后来 and 然后? Could I say 然后又笑了?

Both can mean “then / afterwards”, but:

后来 is usually used when talking about what happened later in the past, often with some separation in time or narrative.
然后 is more like “and then / next” in a step‑by‑step sequence; it can be used in instructions, stories, etc., and isn’t limited to the past.

In this sentence, 后来 is very natural because we’re narrating past events.
然后又笑了 is also grammatical and understandable; it just feels a bit more like a simple “and then she laughed” without emphasizing the “later on (change of mood)” feel as much as 后来 does.

Why is it 又笑了 and not 再笑了? What’s the difference between 又 and 再?

Both 又 and 再 can translate as “again”, but they differ:

又 usually refers to something happening again in the past or present.
It often carries a nuance of repetition or another occurrence that actually happened.
再 is often used for future / hypothetical repetition: “do it again (later)”.

Here, she already cried and then later laughed again, so we use 又:

她先哭了一会儿，后来又笑了。
= She first cried for a while, and later (she) laughed again.

If you said 再笑了, it would sound unusual here; 再 is more like “(will) do it again” in the future or as a request.

Why is 了 used after both 哭 and 笑? What does that 了 mean?

The 了 here is the verb‑following aspect particle, marking a completed action.

哭了一会儿 = “cried (for a while)” – the crying happened and finished.
笑了 = “laughed / started laughing” – the laughing happened.

This kind of 了 comes right after the verb or verb phrase.
It’s different from the sentence‑final 了, which often marks a change of situation or new state.
You can have both types of 了 in one sentence, but here we only see the verb‑aspect 了 twice.

What does 一会儿 mean in 哭了一会儿? Why is there no measure word like 一个会儿?

一会儿 means “a little while / a short time” and it already functions as a set time expression, so no extra measure word is needed:

哭了一会儿 = “cried for a little while”

You don’t say 一个会儿 in standard Mandarin.
Other similar duration phrases also don’t add extra measure words, e.g.:

等一会儿 – wait a moment
玩一会儿 – play for a while

How is 一会儿 pronounced? What is that 儿 sound doing there?

一会儿 is pronounced yíhuìr in standard Mandarin:

一 (yī) changes to yí because of tone sandhi before a fourth tone (会 huì).
The 儿 (r) adds “er‑hua” – an r‑colored sound common in northern Mandarin (especially Beijing).

In southern accents, people may say it without the 儿: yíhuì.
In standard (Putonghua), 一会儿 (yíhuìr) is the usual form, but if you say 一会 (yíhuì) people will still understand you.

Can the sentence be shortened by omitting some parts like 在 or 跟?

You can’t naturally drop 在 or 跟 here without changing the structure:

✗ 火车站朋友说再见的时候… – sounds wrong; it loses the clear relationship markers.
You need 在 to mark location (在火车站), and 跟 (or 和) to mark the person you’re with (跟朋友).

However, in context, you might drop some things if they’re very obvious from previous sentences, e.g. just say:

说再见的时候，她先哭了一会儿…

But in this single stand‑alone sentence, 在 and 跟 should stay.

Is there any difference between 时候 and 时间? Why do we use 时候 here?

Yes, they’re different:

时候 = “when / time (at which something happens)”, used with specific situations or clauses:
我来的时候 – “when I came”
时间 = “time” in a more general, abstract sense, often used with 有 / 没有:
我没有时间 – “I don’t have time”

In 在火车站跟朋友说再见的时候, we’re talking about the moment when she said goodbye, so 时候 is the correct word, not 时间.