junbiga doemyeon mesijiro allyeo juseyo.

Literally, it is something like when the preparation becomes complete / when readiness is achieved.

A more natural English explanation is when you’re ready or once you’re ready.

Why it works this way:

• 준비 = preparation, readiness
• 되다 = to become, to be done
• 준비가 되다 = to become ready / to be ready
• -면 = if/when

So 준비가 되면 is a very common Korean way to say when ready.

In 준비가 되다, 가 marks 준비 as the thing that becomes complete or achieved.

This is a very common pattern:

• 준비를 하다 = to prepare
• 준비가 되다 = to be ready / for preparations to be complete

So:

• 준비를 하다 focuses on doing the preparation
• 준비가 되다 focuses on the state of being ready

That is why 준비가 되면 sounds natural here.

It can mean either, depending on context.

In this sentence, -면 is best understood as when or once, because the speaker expects the condition to happen.

So although -면 is grammatically a conditional ending, here it feels like:

• when you’re ready
• once you’re ready

If the situation were more uncertain, it could feel more like if.

Because -로 marks the method, means, or channel.

So 메시지로 알려 주세요 means:

• please let me know by message
• please inform me via message

If you used 메시지를, that would make message the direct object, which would change the meaning.

Compare:

• 메시지로 알려 주세요 = let me know by message
• 메시지를 알려 주세요 = tell me the message or inform me of the message
  This is not what the sentence is trying to say.

So -로 is important here because it shows how the person should contact you.

알려 주세요 means please let me know, please tell me, or please inform me.

It comes from 알리다 meaning to inform / to notify, plus -어 주세요, which makes a polite request.

So:

• 알리다 → 알려
• 알려 주세요 = please inform me/us

This expression is extremely common in Korean.

It is often better translated as let me know rather than a very literal inform me, because that sounds more natural in English.

It is omitted because Korean often leaves out things that are obvious from context.

In English, you usually need me:

• Please let me know

In Korean, the listener can understand who should be informed, so 저에게, 제게, or 저한테 is often dropped.

A fuller version would be:

• 준비가 되면 저에게 메시지로 알려 주세요.

But in everyday Korean, leaving it out is completely natural.

It is polite and standard, suitable for many everyday situations.

It sounds respectful without being overly formal.

Compare:

• 알려 줘 = casual, used with close friends or someone younger
• 알려 주세요 = polite, everyday standard
• 알려 주십시오 = more formal, stiffer, often used in announcements or business situations

So 준비가 되면 메시지로 알려 주세요 is a normal polite request.

Yes. In many contexts, 메시지 can mean a text, chat message, DM, or similar electronic message.

The exact type depends on context.

For example:

• 메시지 = general message
• 문자 = specifically an SMS text message

So if the speaker just wants a written message of some kind, 메시지로 works well.

The standard spacing is 알려 주세요.

That is because 주다 is functioning like a separate helping verb in the -아/어 주다 pattern.

So standard writing is:

• 알려 주세요
• 도와 주세요
• 보내 주세요

However, in real-life texting, signs, and online writing, you will very often see:

• 알려주세요
• 도와주세요
• 보내주세요

So:

• 알려 주세요 = standard spacing
• 알려주세요 = very common in practice

Yes, you could, and it would sound natural too.

There is a small difference in feel:

• 준비가 되면 emphasizes when you are in a ready state
• 준비되면 is a more compact verbal form meaning when it gets prepared / when it’s ready

In many everyday situations, the two are very close in meaning.

The version in your sentence, 준비가 되면, is especially common when talking about a person being ready to proceed.