Dis nie dat hulle praat nie—net dat hulle lees.

Dis is the contracted form of Dit is, meaning it is.

So:

• Dis = Dit is
• Dis nie ... nie = It is not ...

This contraction is extremely common in everyday Afrikaans, both in speech and in informal writing.

Afrikaans normally uses a double negative frame:

• the first nie appears earlier in the clause
• the second nie appears near the end of the clause

So in Dis nie dat hulle praat nie:

• first nie comes after is in Dis
• second nie closes the negative clause

These two nies work together. They do not cancel each other out the way two negatives might in logic or in some forms of English.

Dat means that and introduces a subordinate clause.

So:

• dat hulle praat = that they are talking / that they talk
• dat hulle lees = that they are reading / that they read

In this sentence, the pattern Dis nie dat ... nie is a very common way to say It’s not that ...

Afrikaans usually does not use a separate verb like English am/is/are to form the ordinary present continuous.

So:

• hulle praat can mean they talk or they are talking
• hulle lees can mean they read or they are reading

Context tells you which meaning is intended.

If you really want to stress that an action is in progress, Afrikaans can use:

• hulle is besig om te lees = they are busy reading / they are reading

But in many ordinary sentences, the simple present is enough.

After dat, Afrikaans uses subordinate clause word order, where the verb goes to the end of the clause.

That is why you get:

• dat hulle praat
• dat hulle lees

If there were more words, the verb would still stay at the end:

• dat hulle Afrikaans praat
• dat hulle die boek lees

This is different from normal main-clause word order.

Here they are finite present-tense verbs.

Afrikaans often uses the same basic form for:

• the infinitive
• the present tense

So the form itself does not always tell you the difference. The sentence structure tells you.

In dat hulle praat and dat hulle lees, these are finite verbs because they belong to clauses with a subject, hulle.

Net here means just, only, or simply.

So net dat hulle lees means something like:

• just that they are reading
• only that they are reading

It softens or corrects the first idea:

• not that they are talking
• just that they are reading

It is left out because Afrikaans often omits repeated words when the meaning is already clear.

The fuller version would be:

• Dis nie dat hulle praat nie—dis net dat hulle lees.

But after the dash, dropping the second dis sounds natural and avoids repetition.

This kind of omission is very common in both English and Afrikaans.

The dash marks a strong contrast or correction.

It signals something like:

• not X — just Y

So the sentence first rejects one explanation, then immediately gives the right one.

A comma could sometimes be used in similar writing, but the dash makes the contrast feel sharper and more deliberate.

In Afrikaans, verbs usually do not change form for different persons in the present tense.

So you get:

• ek praat
• jy praat
• hy praat
• hulle praat

The verb stays the same. This is much simpler than English, where you have forms like I read but he reads.

Yes. It is a very useful pattern.

You can use it whenever you want to say It’s not that ...

For example:

• Dis nie dat ek moeg is nie; ek is net besig.
  = It’s not that I’m tired; I’m just busy.

• Dis nie dat sy kwaad is nie—sy is net stil.
  = It’s not that she’s angry—she’s just quiet.

So the sentence you were given is a good model for a common Afrikaans structure.