Ons tel af voordat die skattejag begin.

Because aftel is a separable verb in Afrikaans.

• The full dictionary form is aftel = to count down
• In a normal main clause, it splits:
  • Ons tel af
• In some other structures, it can stay together:
  • om af te tel
  • aftelling = countdown

So in this sentence, tel is the verb part and af is the separated particle.

Tel af means to count down.

Literally:

• tel = count
• af often adds the idea of completion, downward movement, or counting off

So Ons tel af means We are counting down or We count down.

It is a very common expression for:

• a launch
• New Year’s Eve
• the start of a game or event

Yes, ons means we.

Some basic subject pronouns in Afrikaans are:

• ek = I
• jy / u = you
• hy = he
• sy = she
• ons = we
• julle = you plural
• hulle = they

In this sentence, ons is simply the subject: we.

A useful thing to know is that Afrikaans verbs usually do not change form much depending on the subject. So:

• Ek tel af
• Ons tel af
• Hulle tel af

The verb tel stays the same.

Voordat means before when it introduces a clause with its own subject and verb.

Here, what follows is a full clause:

• die skattejag begin
• the treasure hunt begins

So voordat is the correct choice.

Compare:

• voor die skattejag = before the treasure hunt
  
  • here voor is followed only by a noun phrase
• voordat die skattejag begin = before the treasure hunt begins
  
  • here voordat is followed by a clause

So the difference is much like:

• before the treasure hunt
• before the treasure hunt begins

Because voordat introduces a subordinate clause, and in Afrikaans subordinate clauses usually send the finite verb to the end.

So:

• Main clause: Ons tel af
• Subordinate clause: voordat die skattejag begin

This is a very important Afrikaans pattern.

More examples:

• Ek bly tuis omdat ek moeg is.
• Sy kom wanneer die klas klaar is.

In subordinate clauses, Afrikaans often has a more German/Dutch-like word order, with the verb later or at the end.

Afrikaans verbs generally do not change form for different subjects in the present tense.

So you get:

• ek begin
• jy begin
• hy begin
• ons begin
• hulle begin

Unlike English, Afrikaans does not usually add -s for he/she/it, and unlike Dutch, it does not use forms like begint.

That is why die skattejag begin is correct.

Skattejag is a compound noun:

• skatte = treasures
• jag = hunt

So skattejag literally means treasure hunt.

Afrikaans often forms compound nouns this way, just like Dutch and German, and often like English too.

Other examples:

• huiswerk = homework
• sonbril = sunglasses
• tafeldoek = tablecloth

So once you get used to compounds, they become much easier to recognize.

Die is the definite article in Afrikaans, meaning the.

So:

• die skattejag = the treasure hunt

One useful feature of Afrikaans is that die is used for all genders and for both singular and plural definite nouns in most ordinary cases.

So unlike languages with separate masculine/feminine/neuter articles, Afrikaans keeps it simple here.

Examples:

• die boek = the book
• die vrou = the woman
• die kinders = the children

Yes. The Afrikaans present tense can often cover both:

• We count down
• We are counting down

So Ons tel af voordat die skattejag begin could mean:

1. a general or repeated action:
   We count down before the treasure hunt begins
2. something happening now, depending on context:
   We’re counting down before the treasure hunt begins

Context usually tells you which meaning is intended.

Yes — this sentence shows two very common Afrikaans patterns:

1. Separable verbs

   • aftel → tel af

2. Subordinate clause word order

   • voordat die skattejag begin
   • the verb begin moves to the end

If you can recognize those two patterns, you will understand a lot of everyday Afrikaans much more easily.