Voordat ons vertrek, maak ek my reënjas vas.

Voordat means before when it introduces a whole clause, not just a noun.

So:

• voordat ons vertrek = before we leave
• voor die reis = before the trip

Use voordat when something follows with its own subject and verb, like ons vertrek.

The part Voordat ons vertrek is a subordinate clause placed at the beginning of the sentence. In Afrikaans, it is normal to separate that opening clause from the main clause with a comma.

So the sentence is divided like this:

• Voordat ons vertrek, = time clause
• maak ek my reënjas vas. = main clause

This is because Afrikaans follows a verb-second pattern in main clauses. If something comes first before the main clause, the finite verb comes next.

Here, Voordat ons vertrek comes first, so in the main clause the verb must come immediately after that:

• Voordat ons vertrek, maak ek my reënjas vas.

If the sentence started directly with the subject, you would get:

• Ek maak my reënjas vas voordat ons vertrek.

So both patterns are normal; the word order changes because of what comes first.

Maak ... vas is a common Afrikaans verb expression meaning fasten, tie up, do up, or secure, depending on context.

In this sentence, it means something like I fasten my raincoat or I do up my raincoat.

The word vas adds the idea of something being fixed or secured.

Because maak ... vas is a separable verb expression. In a normal main clause, the conjugated verb maak appears earlier in the sentence, while vas moves to the end.

So:

• Ek maak my reënjas vas.

This is very common in Afrikaans with separable verbs and verb-particle combinations.

No. It often splits in main clauses, but it stays together in some other structures.

For example:

• Main clause: Ek maak my reënjas vas.
• Infinitive: Ek wil my reënjas vasmaak.
• With te: Dit is maklik om my reënjas vas te maak.
• Past participle: Ek het my reënjas vasgemaak.

So learners need to recognize both the separated and joined forms.

Yes. Here my is the possessive word meaning my.

• my reënjas = my raincoat

Afrikaans uses my both as:

• a possessive determiner: my jas = my coat
• an object pronoun: Hy sien my = He sees me

So the form is the same, but the function depends on where it appears in the sentence.

Here vertrek is a verb meaning leave or depart.

So:

• ons vertrek = we leave / we depart

You may also see vertrek as a noun meaning room, but that is a different use. In this sentence, after the subject ons, it is clearly the verb.

The ë shows that the vowels are pronounced separately.

So reënjas is pronounced roughly like:

• re-en-jas

The dots tell you that this is not one single vowel sound. Afrikaans uses this mark, called a diaeresis, to make pronunciation clearer in words like this.

Yes, absolutely. That is also correct.

The difference is mainly emphasis and sentence flow:

• Voordat ons vertrek, maak ek my reënjas vas.
  This puts the time idea first: Before we leave...
• Ek maak my reënjas vas voordat ons vertrek.
  This starts with the action: I fasten my raincoat...

Both are natural Afrikaans.