As jou knie weer begin bloei, moet jy onmiddellik die dokter bel.

Here As introduces a condition, so it usually means if.

In a medical or safety instruction like this, English might also translate it as when if the speaker expects the situation to happen, but grammatically as is the normal Afrikaans word for if in this kind of sentence.

So:

• As jou knie weer begin bloei ... = If your knee starts bleeding again ...

Jou means your, while jy means you.

So:

• jy = you
• jou = your / you

Because knie is a noun, you need the possessive form:

• jou knie = your knee

You would not say jy knie because that would be like saying you knee in English.

Weer means again.

So:

• jou knie weer begin bloei = your knee starts bleeding again

It comes before begin bloei in this sentence, which is a normal place for an adverb in Afrikaans.

Because after As, Afrikaans uses subordinate clause word order, where the finite verb usually goes to the end of the clause.

Compare:

• Main clause style: Jou knie begin weer bloei.
• After As: As jou knie weer begin bloei ...

So the verb begin moves toward the end because the clause is introduced by As.

That is one of the most important word-order patterns in Afrikaans.

After verbs like begin, Afrikaans often uses another verb directly without te.

So:

• begin bloei = begin to bleed

This is very normal Afrikaans.

You may also sometimes see begin om te bloei, but begin bloei is shorter and very common.

Bloei means to bleed.

In this sentence:

• begin bloei = start bleeding

It is the infinitive/base form of the verb, and after begin it stays in that form.

Because the sentence begins with a subordinate clause:

• As jou knie weer begin bloei, ...

After that whole clause comes first, the main clause uses inversion, so the verb comes before the subject:

• moet jy onmiddellik die dokter bel

This is very common in Afrikaans.

Compare:

• Jy moet die dokter bel. = You must call the doctor.
• As ..., moet jy die dokter bel. = If ..., you must call the doctor.

So moet jy is required by the word order after the fronted As clause.

Because moet is a modal verb, and in Afrikaans the second verb usually goes to the end of the clause.

So the structure is:

• moet = must
• bel = call

That gives:

• moet jy onmiddellik die dokter bel

This is similar to other Afrikaans modal patterns:

• Ek kan Afrikaans praat. = I can speak Afrikaans.
• Sy wil huis toe gaan. = She wants to go home.

The main/modal verb comes earlier, and the other verb goes to the end.

Onmiddellik means immediately.

In this sentence it comes before die dokter:

• moet jy onmiddellik die dokter bel

That placement is natural and common.

You may sometimes see adverbs moved around for emphasis, but this version is standard and clear.

Die dokter means the doctor, while 'n dokter means a doctor.

So the sentence is talking about a specific doctor, or at least the doctor in the situation, not just any doctor.

Compare:

• Bel die dokter. = Call the doctor.
• Bel 'n dokter. = Call a doctor.

Both are possible Afrikaans, but they mean slightly different things.

Usually yes. Moet often means must / have to / need to, depending on context.

In a sentence like this, it gives strong advice or instruction:

• moet jy onmiddellik die dokter bel = you must / should call the doctor immediately

In real translation, English might choose must, should, or need to depending on tone, but moet itself is the standard strong form.

Knie is pronounced roughly like knee in English.

Important point: the k is not pronounced.

So:

• knie sounds like nee / knee

That silent k also appears in some related words, just as in English.

Yes, you could.

The difference is:

• As jou knie weer begin bloei = If your knee starts bleeding again
• As jou knie weer bloei = If your knee is bleeding again / bleeds again

Using begin focuses on the start of the bleeding. Without begin, the sentence is a little less specific about the exact moment and just refers to the bleeding happening again.

Yes, in real usage as can sometimes be translated as when, depending on context.

But for learners, the safest first understanding is:

• as = if

In a sentence like this, English may choose if or when depending on how certain the speaker thinks the event is. The Afrikaans structure itself is completely normal either way.