Toe ek die verkeerde adres lees, het ek agtergekom hoekom die aflewering laat was.

Here toe means when.

Afrikaans toe can also mean then in other sentences, but in this sentence it introduces a time clause:

Toe ek die verkeerde adres lees = When I read the wrong address

A useful clue is that toe is followed by a full clause, not just used as an adverb.

Because Toe ek die verkeerde adres lees is a subordinate clause.

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

• Toe = when
• ek = I
• die verkeerde adres = the wrong address
• lees = read

That is normal Afrikaans word order after conjunctions like toe, omdat, dat, terwyl, and so on.

This is a very common question.

After toe, Afrikaans often uses the simple verb form in storytelling or narrative past context, even though English would use a past form:

• Toe ek die verkeerde adres lees...
  literally looks like When I read / read
• but it naturally means When I read the wrong address... in the past

The past meaning is understood from toe and the rest of the sentence.

You may also see fuller past constructions in other contexts, but this shorter pattern with toe + simple verb at the end is very common and natural.

Because Afrikaans main clauses follow a verb-second pattern.

When the sentence starts with something other than the subject, the finite verb comes first, then the subject. Here, the whole toe clause comes first:

Toe ek die verkeerde adres lees, | het | ek | agtergekom ...

So the structure is:

• first position: the whole time clause
• second position: het
• then: ek

If the sentence started with ek, then you would get:

Ek het agtergekom ...

Agtergekom is the past participle of agterkom, which means to realize, to find out, or to figure out.

So:

• agterkom = infinitive / dictionary form
• agtergekom = past participle

In the perfect tense, Afrikaans often uses:

het + past participle

So:

het ek agtergekom = I realized / I found out

This verb is treated as one unit: agterkom.
In a finite clause, the pieces may appear separated by word order, but it is still one verb.

Because this is an indirect question, not a direct question.

Direct question: Hoekom was die aflewering laat?
= Why was the delivery late?

Indirect question: ... hoekom die aflewering laat was
= ... why the delivery was late

In indirect questions, Afrikaans uses subordinate clause word order, so the verb goes to the end:

• hoekom
• die aflewering
• laat
• was

Was is the past form of is from the verb wees.

So:

• is = is
• was = was

Since the sentence is talking about a past situation, was is the correct form:

die aflewering laat was = the delivery was late

And because this is inside an indirect question introduced by hoekom, was moves to the end.

Because the adjective comes before the noun.

In Afrikaans, an adjective before a noun usually takes -e:

• die verkeerde adres = the wrong address

But when the adjective comes after a linking verb, it usually has no -e:

• Die adres is verkeerd = The address is wrong

So:

• before the noun: verkeerde
• after is: verkeerd

Yes, often it could.

Both hoekom and waarom can mean why.
But hoekom is very common in everyday speech, while waarom can sound a bit more formal or written, depending on context.

So this sentence could also be understood with waarom, but hoekom sounds very natural here.

Because the sentence begins with a subordinate clause:

Toe ek die verkeerde adres lees, ...

In Afrikaans, when a subordinate clause comes before the main clause, it is normally separated by a comma.

So the comma marks the boundary between:

• the time clause: Toe ek die verkeerde adres lees
• the main clause: het ek agtergekom hoekom die aflewering laat was

Because Afrikaans does not form every past meaning in exactly the same way.

Very often, Afrikaans uses the perfect pattern:

• het + past participle
• het ek agtergekom

But some very common verbs, especially wees, also use a simple past form:

• is → was

So in one sentence, it is completely normal to have:

• het ek agtergekom = I realized
• die aflewering laat was = the delivery was late

That mixture is standard Afrikaans.