As dit reën, neem ek my sambreel saam.

It can mean either, depending on context.

In As dit reën, neem ek my sambreel saam, as often has the sense of if/when in a general situation:

• If it rains, I take my umbrella with me
• When it rains, I take my umbrella with me

So this sentence can describe a habit or a general rule.

If you want to be more clearly temporal, Afrikaans also often uses wanneer for when:

• Wanneer dit reën, neem ek my sambreel saam.

Because As dit reën is a subordinate clause.

In Afrikaans, subordinate clauses usually send the finite verb to the end. So:

• Main clause: Dit reën
• Subordinate clause: as dit reën

This is a very important word-order pattern in Afrikaans:

• Ek bly by die huis.
• As dit reën, bly ek by die huis.

So the final position of reën is caused by as introducing a subordinate clause.

Because the sentence begins with the subordinate clause, and the main clause then follows normal verb-second word order.

The first position in the whole sentence is occupied by the clause As dit reën. That means the verb of the main clause must come next:

• As dit reën, neem ek my sambreel saam.

Compare:

• Ek neem my sambreel saam as dit reën.
• As dit reën, neem ek my sambreel saam.

Both are correct. The difference is just word order.

Here saam means something like along or with me.

The expression saamneem / neem ... saam means to take along or to bring along.

So:

• Ek neem my sambreel. = I take my umbrella.
• Ek neem my sambreel saam. = I take my umbrella along / with me.

In practice, saam often adds the idea that you are taking something with you rather than just taking hold of it.

Yes, effectively it behaves like a separable verb.

In a main clause, the parts are split:

• Ek neem my sambreel saam.

In forms where the verb cluster stays together, you may see:

• om my sambreel saam te neem
• Ek wil my sambreel saamneem or saam neem
  (spelling can vary by style and dictionary preference)

For a learner, the key thing is to recognize that neem ... saam works as one meaning unit: take along.

Because Afrikaans, like English, uses a dummy subject with weather verbs.

So:

• Dit reën. = It is raining / It rains.
• Dit sneeu. = It is snowing.

The dit does not refer to a real thing. It is just there because the sentence structure needs a subject.

Because Afrikaans possessive adjectives do not change for gender, number, or case.

So my always stays my:

• my boek
• my sambreel
• my vriend
• my vriende

That is much simpler than in many other languages.

Also, sambreel is a common Afrikaans word for umbrella.

The two dots in reën show that the vowels are pronounced separately, not as one combined sound.

So reën is pronounced roughly like ree-un in two syllables.

The diaeresis helps you avoid reading it as one long vowel sequence. You will see this in some other Afrikaans words too.

So:

• reën = rain / to rain
• pronounced as two syllables

Yes, normally a comma is used after an introductory subordinate clause in Afrikaans:

• As dit reën, neem ek my sambreel saam.

This comma makes the structure clearer and is standard written punctuation.

Yes. Afrikaans often uses the present tense for habitual actions, general truths, and even future meaning when the context is clear.

So As dit reën, neem ek my sambreel saam can mean:

• a habit: Whenever it rains, I take my umbrella
• a future condition: If it rains, I’ll take my umbrella

Afrikaans does not always need a separate future form where English would use will.

Yes, absolutely.

That version is also correct:

• Ek neem my sambreel saam as dit reën.

The difference is mainly emphasis and sentence flow:

• As dit reën, neem ek my sambreel saam.
  Starts with the condition, so it highlights if/when it rains.

• Ek neem my sambreel saam as dit reën.
  Starts with I take my umbrella along, then adds the condition.

Both are natural Afrikaans.