nǐ xiān zài wàimiàn děng wǒ, wǒ hěnkuài jiù chūlái.

先 means first, before that, or for now.

In this sentence, 你先在外面等我 means something like:

• Wait outside first
• Go wait outside for now

It tells the listener to do that action before the speaker does the next action in the second clause.

This follows a very common Mandarin pattern:

subject + sequence/time word + location + verb + object

So here you get:

• 你 = subject
• 先 = first / for now
• 在外面 = outside
• 等 = wait
• 我 = me

So literally it is close to:

You first outside wait for me.

That sounds strange in English, but it is normal Chinese word order. Mandarin usually puts words like 先 before the main action, and location phrases like 在外面 before the verb too.

在 + place often tells you where an action happens.

So:

• 在外面等我 = wait for me outside

Here, 在 marks the location of the waiting.

Without 在, the sentence would not sound right in standard Mandarin here. The normal structure is 在 + location + verb.

外面 literally means the outside / the outer side / outside.

In this sentence, it means outside relative to wherever the speaker is now, such as:

• outside the room
• outside the office
• outside the building

It is a physical location word. A very similar word is 外边, which often means the same thing in everyday speech.

There is no separate word for for here, because 等 can take a direct object in Chinese.

So:

• 等我 = wait for me
• literally: wait me

This is very common in Mandarin. English often uses a preposition, but Chinese often does not.

Other similar examples:

• 找你 = look for you
• 帮我 = help me

So 等我 is completely normal.

很快就 means something like very soon or in just a moment.

Breakdown:

• 很快 = very fast / very soon
• 就 = then / soon / as early as that

In this sentence, 就 adds a sense that the action will happen soon and without much delay.

So 我很快就出来 means:

• I’ll come out very soon
• I’ll be out in a moment

If you remove 就, the sentence is still grammatical, but 就 makes it sound more natural and more reassuring.

This is about direction.

• 出来 = come out
• 出去 = go out

Both use 出, which means out, but the second part matters:

• 来 = movement toward the speaker or toward the conversational reference point
• 去 = movement away from the speaker or away from that reference point

Here the speaker is saying I’ll come out, meaning they will come out and join the listener. So 出来 is the natural choice.

If you used 出去, it would sound more like go out, which has a different viewpoint.

Yes, it is very helpful here, and in this sentence it is the natural choice.

Compare:

• 你先在外面等我，我很快就出来。
• 你先在外面等我，很快就出来。

If you remove the second 我, the second clause can become less clear, because Chinese often assumes the same subject continues unless you mark a new one. After 你先在外面等我, the listener might momentarily expect the subject to still be 你.

By saying 我很快就出来, the speaker clearly marks:

• you wait outside
• I will come out soon

So the second 我 is important for clarity.

It is mostly a request/instruction, followed by a reassurance.

The first clause:

• 你先在外面等我
• Wait outside for me first

This is an imperative-type sentence, but it does not have to sound rude. In normal conversation, it can sound perfectly natural.

The second clause:

• 我很快就出来
• I’ll be out very soon

This softens the situation by explaining that the wait will not be long.

So overall, the tone is often practical and reassuring, not harsh.

A few common ways:

• 你先在外面等我一下，我很快就出来。
• 你先在外面等我一下吧，我很快就出来。
• 请你先在外面等我一下，我很快就出来。

What these add:

• 一下 softens the request and suggests for a moment
• 吧 makes it sound less blunt
• 请 adds politeness, though it can sound a bit formal depending on the situation

A very natural softer version is:

你先在外面等我一下吧，我很快就出来。

The comma separates two closely related clauses:

• 你先在外面等我
• 我很快就出来

Chinese uses commas very often to mark a pause between related ideas. In English, you might use:

• a comma
• a period
• and
• a semicolon

But in Chinese, this comma is very normal and natural.

Yes, 很快 can mean either quickly or soon, depending on context.

In this sentence, it is best understood as soon:

• 我很快就出来 = I’ll come out soon

That is because the sentence is about when the speaker will appear, not about the speed of the physical motion itself.

So although 很快 literally relates to speed, here the natural English meaning is soon.

Yes, one common point is third-tone sandhi.

The important part is:

• 我很 is written wǒ hěn
• but when spoken together, it is pronounced more like wó hěn

That is because when one third tone comes before another third tone, the first one usually changes to a rising tone in actual speech.

So this part sounds like:

• wó hěn kuài jiù chūlái

A few other notes:

• 你 in 你先 stays third tone, because 先 is first tone
• 出来 is chūlái, not neutral tone here

So the sentence is written:

nǐ xiān zài wàimiàn děng wǒ, wǒ hěnkuài jiù chūlái

but in natural speech, the second 我 is often heard as wó because of tone sandhi before 很.