Toe ons die adres weer gelees het, het ons die brief in die posbus gesit.

Here toe means when or after, introducing a past-time clause.

In this sentence, Toe ons die adres weer gelees het means When/After we had read the address again. In other contexts, toe can also relate to then or at that time, but here it is clearly a conjunction meaning when in the past.

Usually no, not in a natural everyday sentence like this.

Toe is the normal choice for a specific event in the past:

• Toe ons die adres weer gelees het ... = When we read the address again ...

Wanneer is more often used for:

• questions: Wanneer kom jy? = When are you coming?
• general or repeated situations
• future-oriented when

So toe is the better and more idiomatic word here.

Because the first part is a subordinate clause introduced by toe.

In Afrikaans subordinate clauses, the finite verb usually goes to the end. Since this clause is in the perfect tense, the participle comes before it:

• gelees = past participle
• het = auxiliary verb

So the pattern is:

Toe + subject + other words + past participle + het

That is why you get:

Toe ons die adres weer gelees het

and not Toe ons het die adres weer gelees.

This is because Afrikaans main clauses follow a verb-second pattern.

The whole first clause, Toe ons die adres weer gelees het, takes the first position in the sentence. After that, the finite verb of the main clause must come next.

So the structure is:

• First position: Toe ons die adres weer gelees het
• Second position: het
• Then the subject: ons

That gives:

Toe ons die adres weer gelees het, het ons die brief in die posbus gesit.

If the sentence started directly with ons, then you would say:

Ons het die brief in die posbus gesit.

Because both clauses are in the perfect tense.

First clause:

• ons ... gelees het = we had read / we read

Main clause:

• het ons ... gesit = we put / we placed

Afrikaans very often uses het + past participle for past actions, so it is completely normal to see het in both clauses.

Because they are past participles.

In Afrikaans, the perfect tense is commonly formed with:

het + past participle

For many verbs, the past participle begins with ge-:

• lees → gelees
• sit → gesit

So:

• het gelees = read / had read
• het gesit = put / placed

Yes, sit often means to sit, but in Afrikaans it can also mean to put or to place, especially in everyday speech.

Here it is transitive, because it takes an object:

• die brief = the thing being put
• in die posbus = where it is put

So het ons die brief in die posbus gesit means we put the letter in the mailbox/postbox.

This is a very normal Afrikaans usage.

Weer means again, and it modifies the action gelees.

In a subordinate clause like this, adverbs such as weer often appear before the participle and before the final het:

Toe ons die adres weer gelees het

That is a natural neutral word order in Afrikaans.

First they read the address again, then they put the letter in the mailbox.

The clause introduced by toe sets up the earlier action:

• Toe ons die adres weer gelees het = first event

Then the main clause gives the next event:

• het ons die brief in die posbus gesit = second event

So the sequence is clear.

Because Afrikaans usually uses the perfect tense for ordinary past events.

Where English often says:

• We read the address again
• We put the letter in the mailbox

Afrikaans normally says:

• Ons het die adres weer gelees
• Ons het die brief in die posbus gesit

So this sentence is not unusually formal or special. It is just standard Afrikaans past-time narration.

No. Afrikaans has one main definite article: die.

It does not change for:

• gender
• most case distinctions
• singular vs. plural

So you get:

• die adres
• die brief
• die posbus

This is much simpler than in languages with different forms such as the, der, die, das, and so on.

Yes, in normal written Afrikaans it should be there.

The first part is an introductory subordinate clause:

Toe ons die adres weer gelees het, ...

The comma marks the boundary before the main clause:

..., het ons die brief in die posbus gesit.

So the punctuation is standard and helpful.

In this sentence, it most naturally means a mailbox/postbox where the letter is placed.

Context matters, because posbus can sometimes also refer to a postal box in other situations. But with die brief in die posbus gesit, most learners should understand it as put the letter into the mailbox/postbox.