Toe haar telefoon gelui het, het sy die koerant op die tafel gesit.

Here toe means when.

So Toe haar telefoon gelui het... means When her phone rang...

A useful extra point: toe can also mean then in other sentences, so the meaning depends on context. In this sentence, it is clearly introducing a past time clause, so when is the right meaning.

Afrikaans usually uses toe for a specific event in the past.

So if you are talking about one completed past moment, toe is natural:

• Toe haar telefoon gelui het... = When her phone rang...

By contrast, wanneer is more often used for:

• general or repeated situations
• questions
• future meaning

For example:

• Wanneer kom sy? = When is she coming?
• Wanneer ek tyd het, lees ek. = When/Whenever I have time, I read.

So in your sentence, toe fits because this is one past event.

Because there are two clauses, and each clause has its own verb structure.

The sentence has:

1. Toe haar telefoon gelui het
2. het sy die koerant op die tafel gesit

Both clauses are in the past, and Afrikaans usually forms the past with:

het + past participle

So:

• gelui het = rang / has rung / had rung depending on context
• het ... gesit = put

English often uses a simple past form like rang or put, but Afrikaans normally uses this het + participle pattern instead.

This is a word-order question.

In the toe clause, the verb is in a subordinate clause, so the finite verb het goes to the end:

• Toe haar telefoon gelui het

In the main clause, Afrikaans uses verb-second word order, so the finite verb comes early:

• het sy die koerant op die tafel gesit

A very useful comparison is this:

• Main clause by itself: Sy het die koerant op die tafel gesit.
• After the toe clause is placed first: Toe haar telefoon gelui het, het sy die koerant op die tafel gesit.

So the difference comes from subordinate clause word order versus main clause word order.

Because the whole toe clause comes first, and Afrikaans still keeps the main clause in verb-second order.

If the sentence were just:

• Sy het die koerant op die tafel gesit.

that would be normal.

But once you put Toe haar telefoon gelui het at the front, that whole clause takes the first slot in the sentence. So the finite verb of the main clause must come next:

• Toe haar telefoon gelui het, het sy die koerant op die tafel gesit.

This is very common in Afrikaans:

• Gister het sy gekom.
• Na ete het ons gegaan.
• Toe die telefoon lui, het sy opgestaan.

In this sentence:

• haar = her
• sy = she

So:

• haar telefoon = her phone
• sy = she

One thing that confuses learners is that sy can also mean his in other contexts:

• sy telefoon = his phone

So how do you know what it means? You look at the grammar:

• before a noun, sy can be possessive: his
• standing as the subject pronoun, sy means she

Here het sy clearly means she.

That is a very common question.

Yes, sit can mean sit, but in Afrikaans it can also be used in a sense like put / set / place, depending on context.

Here it means put because it has a direct object:

• sy het die koerant ... gesit
• she put the newspaper ...

Compare:

• Sy het op die stoel gesit. = She sat on the chair.
• Sy het die boek op die tafel gesit. = She put the book on the table.

So the object helps you see the meaning. If something is being placed somewhere, sit/gesit can mean put/set.

They are past participles.

Their base verbs are:

• lui = ring
• sit = sit / put / set

In the past tense, Afrikaans often uses ge- on the participle:

• lui → gelui
• sit → gesit

So:

• het gelui = rang / has rung
• het gesit = put / set

This ge- pattern is very common in Afrikaans, although not every verb follows it in exactly the same way.

Because Afrikaans uses die as the definite article for basically all nouns.

So:

• die koerant = the newspaper
• die tafel = the table

Unlike English learners of languages such as German or French, you do not have to learn different words for the based on gender. Afrikaans does not do that here.

A helpful basic contrast is:

• die = the
• 'n = a / an

For example:

• die koerant = the newspaper
• 'n koerant = a newspaper

Literally, it is on the table.

But with a verb of placement like gesit, English often understands movement automatically, so the full idea is:

• put it on/onto the table

Afrikaans commonly uses op in this kind of sentence without needing a separate word for onto.

If someone wanted to stress the act of setting it down, they might use a verb like neergesit, but your sentence is already perfectly natural.

Yes, it is standard and natural to use a comma there.

The first part is an introductory time clause:

• Toe haar telefoon gelui het, ...

Then comes the main clause:

• ..., het sy die koerant op die tafel gesit.

So the comma helps separate the two parts clearly. In writing, this is the normal way to present the sentence.