Ons verlaat die park wanneer dit begin reën.

Ons means we here.

A useful extra point: in Afrikaans, ons can mean both we and us, depending on its role in the sentence. In this sentence it is the subject, so it means we.

Verlaat is the normal verb for leave in the sense of leave a place or depart from something.

So:

• Ons verlaat die park = We leave the park

It takes a direct object, just like English leave does.

Also, Afrikaans verbs usually do not change form for different subjects in the present tense, so you get:

• ek verlaat
• jy verlaat
• ons verlaat
• hulle verlaat

The verb stays verlaat.

Die is the definite article, meaning the.

So:

• die park = the park

Afrikaans is simpler than English in one nice way here:

• die is used for the with both singular and plural nouns
• it does not change for gender

Examples:

• die park = the park
• die kinders = the children

Wanneer means when.

In this sentence, it introduces the time clause:

• wanneer dit begin reën = when it starts raining / when it begins to rain

You may also hear as used in some kinds of when sentences in everyday Afrikaans, but wanneer is clear and standard for time. It also helps avoid confusion, because as can also mean if.

So for a learner, wanneer is a very safe and clear choice for when.

Here dit is the same kind of it that English uses in weather expressions.

So:

• dit reën = it is raining / it rains
• dit begin reën = it begins to rain / it starts raining

It does not really refer to a specific thing. It is a dummy subject, just like English it in it is raining.

After begin, Afrikaans often uses the next verb directly, especially in very common expressions.

So:

• dit begin reën = it starts raining

That is very natural Afrikaans.

You may also come across longer forms such as begin om te reën, but begin reën is short, common, and idiomatic.

Because this is a subordinate clause, not a direct question.

• wanneer dit begin reën = when it starts raining
• Wanneer begin dit reën? = When does it start raining?

In the sentence you were given, wanneer is a conjunction introducing a time clause. It is not asking a question, so the word order is different.

That is why you get:

• wanneer + subject + verb(s)
• wanneer dit begin reën

and not the question order:

• wanneer begin dit reën?

Grammatically, it is in the present tense, but Afrikaans present tense often covers meanings that English might express as present, habitual, or future depending on context.

So this sentence can mean something like:

• We leave the park when it starts raining
• We will leave the park when it starts raining

Context tells you which is meant.

If you wanted to make the future more explicit, you could say:

• Ons sal die park verlaat wanneer dit begin reën.

But the original sentence is completely natural.

The two dots are a diaeresis. They show that the vowels are pronounced separately.

So reën is not pronounced as one smooth vowel sound. It is said in two syllables, roughly like ree-uhn.

The dots help show that clearly in writing.

Yes.

Reën can mean:

• rain as a noun
• to rain as a verb

In this sentence, it is a verb, because it follows begin:

• begin reën = start raining

If it were a noun, it would appear in a different structure, for example:

• Die reën is swaar. = The rain is heavy.