Ons steek die verjaarsdagkerse aan sodra die deurklokkie lui.

Because aansteek is a separable verb in Afrikaans.

• The full verb is aansteek = to light / to switch on, depending on context.
• In a main clause, Afrikaans often splits separable verbs:
  • Ons steek die kerse aan.
• In some other structures, the parts stay together:
  • om die kerse aan te steek

So in your sentence, steek ... aan is completely normal.

Here it means to light the birthday candles.

Afrikaans aansteek can be used in different contexts, for example:

• ’n vuur aansteek = light a fire
• kerse aansteek = light candles
• sometimes ’n lig aansteek = switch on a light

In this sentence, because the object is verjaarsdagkerse, the meaning is clearly light the birthday candles.

Afrikaans, like Dutch and German, very often forms compound nouns as one word.

So:

• verjaarsdag = birthday
• kerse = candles
• verjaarsdagkerse = birthday candles

This is very normal in Afrikaans. English often writes similar ideas as two words, but Afrikaans commonly combines them.

Because die can mean both the singular and the plural in Afrikaans.

So:

• die kers = the candle
• die kerse = the candles

Afrikaans does not change the for number the way English changes this/these or that/those.

Sodra means as soon as.

It usually suggests that one action happens immediately after another:

• Ons steek die verjaarsdagkerse aan sodra die deurklokkie lui. = We light the birthday candles as soon as the doorbell rings.

Compare:

• sodra = as soon as
• wanneer = when

Wanneer can be more general, while sodra is more immediate and specific.

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

So:

• Main clause: Ons steek die verjaarsdagkerse aan
• Subordinate clause: sodra die deurklokkie lui

This is one of the most important word-order patterns in Afrikaans.

Compare:

• Main clause: Die deurklokkie lui.
• Subordinate clause: ... sodra die deurklokkie lui.

In this case, lui is already the only verb, so it appears at the end of that clause.

Here lui means rings.

So:

• Die deurklokkie lui. = The doorbell rings.

Be careful: in other contexts, lui can also be related to sounding or tolling, depending on what is making the sound. But in this sentence, rings is the natural translation.

Yes, deurklokkie is a normal and understandable word for doorbell.

It is made up of:

• deur = door
• klokkie = little bell

You may also come across deurbel, which is another common word for doorbell. Both are useful to recognize.

Normally, no. Afrikaans usually requires the subject to be stated.

So you say:

• Ons steek die verjaarsdagkerse aan.

not just:

• Steek die verjaarsdagkerse aan.
  unless it is a command, like Light the birthday candles!

Afrikaans is not like some languages that regularly drop subject pronouns.

Then the verb in the main clause would come before the subject, because Afrikaans uses verb-second word order in main clauses.

So you would get:

• Sodra die deurklokkie lui, steek ons die verjaarsdagkerse aan.

Notice the difference:

• Ons steek ... aan sodra ...
• Sodra ..., steek ons ... aan

This is a very common Afrikaans pattern when a sentence begins with a time clause or another introductory element.

Not in this sentence.

With the separable verb aansteek, the object usually comes between the verb stem and the separable particle in a normal main clause:

• Ons steek die verjaarsdagkerse aan.

Putting aan directly after steek here would sound wrong. The split pattern is:

• steek + object + aan

It is a regular and useful plural to learn:

• kers = candle
• kerse = candles

Many Afrikaans nouns form the plural with -e or -s, and kers → kerse follows a common pattern.

Yes, pretty much.

• deur = door
• klokkie = little bell

The ending -kie is a diminutive ending, so klokkie literally means little bell. Afrikaans uses diminutives very naturally, and many everyday words include them even when English would not.

So although deurklokkie is literally something like door little bell, the natural English meaning is simply doorbell.