Learn Hardcore Chinese: tā zài jùhuì shàng xiān jiǎndān jièshào le zìjǐ, ránhòu jiù gēn dàjiā liáotiān. - At the get-together he first briefly introduced himself, and then started chatting with everyone.

在 marks the general location.
上 here doesn’t mean “on top of” physically; it extends to:
- events: 在会议上 (at the meeting), 在演讲上 (at the speech)
- abstract spaces/media: 在网上 (online / on the internet), 在课上 (in class)

With 聚会 (a gathering/party), native speakers naturally say 在聚会上.

You might see 在聚会 in casual speech, but 在聚会上 is more standard and sounds more complete/natural in most contexts.

What is the role of 先 and where should it go in the sentence?

先 means first or beforehand and marks the first step in a sequence.

Pattern: 先 … 然后 … = first … then …

In this sentence:

先简单介绍了自己 = first (he) briefly introduced himself

Placement:

先 goes before the verb or verb phrase it modifies:
- 先介绍自己
- 先简单介绍自己
You would not say 介绍先自己 or place 先 after 了.

You can move the whole adverbial chunk around a bit:

他在聚会上先简单介绍了自己 (original)
他先在聚会上简单介绍了自己 (also okay) But 先 still comes before the main action (介绍).

Why is 简单 used without 地? Should it be 简单地介绍?

Both 简单介绍 and 简单地介绍 are grammatically correct.

简单介绍 is very common and natural in spoken and written Chinese.
- Here 简单 functions like an adverb meaning briefly / simply, modifying 介绍.
- Many disyllabic adjectives are often used adverbially without 地 in everyday Chinese, especially in set combinations like:
  - 认真学习 (study seriously)
  - 仔细看 (carefully look)
  - 简单介绍 (briefly introduce)
简单地介绍:
- Sounds a bit more formal or careful.
- Slightly stronger emphasis on the manner of the action.

For most ordinary contexts, 简单介绍 is the default, natural choice.

What exactly does 介绍了自己 mean, and how is it different from 自我介绍?

Both express the idea of “introducing oneself,” but the structures are different:

介绍自己
- Literally: introduce oneself.
- 介绍 (to introduce) + 自己 (oneself, reflexive pronoun).
- Example: 他先介绍自己，然后就跟大家聊天。
自我介绍
- A set phrase/compound verb meaning to introduce oneself.
- Very common in formal contexts: interviews, first day of class, speeches.
- Examples:
  - 请大家做一下自我介绍。 (Please everyone give a brief self‑introduction.)
  - 他先做了一个自我介绍。

In your sentence, 介绍了自己 focuses on the action “introduced himself.”
If you said:

他在聚会上先做了自我介绍，然后就跟大家聊天。

it would sound slightly more formal and like “He first gave a self‑introduction at the party, and then chatted with everyone.”

What does 了 do in 介绍了自己? How would the meaning change without 了?

The 了 here is the aspect particle marking a completed action.

介绍了自己 = introduced himself (the action happened and was completed).
In narrative contexts (like telling what happened at a party), 了 is very natural.

If you remove 了:

他在聚会上先简单介绍自己，然后就跟大家聊天。

this is still understandable, but:

It feels less clearly like a specific, completed past event.
It could sound more like a general description of what he typically does at parties, depending on context.

In a specific-story / what‑happened sequence, native speakers strongly prefer 了 after the first completed action here.

What does 就 add in 然后就跟大家聊天? Can we just say 然后跟大家聊天?

然后就… is a very common pattern.

然后 = then / afterwards (marks the next step in a sequence).
就 adds a nuance of:
- immediacy (and then he went right on to…)
- natural/resulting next step (so then he (naturally) just…)

So:

然后就跟大家聊天。
- Feels like: and then (right after that / so next) he started chatting with everyone.

If you say 然后跟大家聊天 (without 就):

Still grammatical.
Slightly more “bare” and neutral, with less feeling of smooth, natural progression.

In colloquial narrative, 然后就… is very typical.

Why isn’t 他 repeated in the second clause? Why not 然后他就跟大家聊天?

In Chinese, when two clauses share the same subject, the subject is often omitted in the second clause, especially if it’s very clear from context.

First clause: 他在聚会上先简单介绍了自己
→ subject = 他
Second clause: 然后就跟大家聊天
→ subject is understood to still be 他, so it can be dropped.

You can say:

然后他就跟大家聊天。

This is also correct, just a bit more explicit and sometimes slightly more formal or literary depending on the style. Omitting 他 here is very natural in everyday speech and writing.

What is the function of 跟 in 跟大家聊天? Can I use 和 instead?

Here 跟 means with:

跟大家聊天 = chat with everyone.

You can usually replace 跟 with 和 when it means with someone:

和大家聊天 is also correct and natural.

Nuance:

跟 is very common in spoken Mandarin for “with” in actions:
- 跟他一起去 (go together with him)
- 跟老师讨论 (discuss with the teacher)
和 is slightly more neutral and is also used for:
- connecting nouns (A 和 B) = A and B
- “with” in some contexts

In this sentence, 跟大家聊天 and 和大家聊天 are both fine; 跟 just feels a bit more colloquial.

What does 大家 mean here? Is it the same as 每个人?

大家 literally means everyone or all of you/us/them as a group.
- 跟大家聊天 = chat with everyone (as a group).
每个人 literally means each person / everyone individually.
- 跟每个人聊天 = chat with each person (one by one).

So:

跟大家聊天: He’s mixing and chatting with the group (may or may not talk to each individual).
跟每个人聊天: Emphasizes that he spoke with each person.

In a typical party description, 跟大家聊天 is the most natural way to say “chatting with everyone.”

How does 聊天 work grammatically? Why is there no object after it?

聊天 is usually treated as an intransitive verb (or a verb-object compound) meaning to chat / to have a chat.

Common patterns are:

跟/和 + person + 聊天
- 跟大家聊天 (chat with everyone)
- 跟朋友聊天 (chat with friends)
聊天 by itself, with no object:
- 我们在咖啡馆聊天。 (We’re chatting in a café.)

If you want to specify the topic, you normally drop 天 and use 聊 + topic:

聊工作 (chat about work)
聊音乐 (talk about music)
跟他聊中国文化 (talk with him about Chinese culture)

So 跟大家聊天 is complete; it doesn’t need another object after 聊天.

Is the word order 他在聚会上先简单介绍了自己 fixed? Can we move things like 在聚会上 or 先 around?

Chinese has a preferred order, but there is some flexibility. A common template is:

Subject + (time) + (place) + (manner) + verb + object

In your sentence:

他 (subject)
在聚会上 (place)
先 (sequence adverb)
简单 (manner)
介绍 (verb)
了自己 (object with aspect marker)

Natural variants include:

他在聚会上先简单介绍了自己。 (original)
他先在聚会上简单介绍了自己。 (also fine)
他先简单在聚会上介绍了自己。 (this sounds awkward; splitting 简单 from 介绍 is not natural)

You generally:

Keep 先 close to the verb phrase it modifies.
Keep 简单 right before 介绍 (they form a tight unit: 简单介绍).

What does the combination 先…然后… express overall in this sentence?

The pair 先…然后… explicitly marks a two-step sequence of actions:

先简单介绍了自己
→ first, he briefly introduced himself
然后就跟大家聊天
→ then he (immediately/naturally) chatted with everyone

So the structure:

先 + Action A，然后(就) + Action B

means:

First do A, then do B.

In narrative Chinese, this is a very common, clear way to describe the order in which things happened.