Voordat de vergadering begint, maak ik mijn werkplek schoon.

Voordat means before when it introduces a full clause.

So in Voordat de vergadering begint, the meaning is Before the meeting begins.

It is written as one word because here it is a fixed conjunction. Dutch often writes these conjunctions as single words.

Because voordat is a subordinating conjunction. In Dutch, a subordinate clause usually sends the conjugated verb to the end.

So:

• de vergadering begint = the meeting begins
• after voordat: voordat de vergadering begint

This is very normal Dutch word order.

Because the subject is de vergadering, which is singular: the meeting.

The verb is beginnen = to begin.
In the present tense, with a singular third-person subject, it becomes begint.

So:

• ik begin = I begin
• jij begint = you begin
• de vergadering begint = the meeting begins

This is because Dutch main clauses follow the verb-second rule.

When the sentence starts with something other than the subject, such as the subordinate clause Voordat de vergadering begint, the conjugated verb comes next, and the subject comes after it.

So:

• normal order: Ik maak mijn werkplek schoon.
• after a fronted clause: Voordat de vergadering begint, maak ik mijn werkplek schoon.

This is called inversion.

Because schoonmaken is a separable verb.

The full verb is:

• schoonmaken = to clean

In a main clause with a conjugated verb, Dutch often splits separable verbs:

• Ik maak mijn werkplek schoon.

But in the infinitive, it stays together:

• Ik wil mijn werkplek schoonmaken.

And in the past participle, it also stays together:

• Ik heb mijn werkplek schoongemaakt.

Here, schoonmaken means to clean or to clean up.

It does not literally mean to make clean in a strange or unnatural way, even though that is the literal breakdown:

• schoon = clean
• maken = make

As a whole, it is just the normal Dutch verb for cleaning something.

Because vergadering is a de-word in Dutch.

You usually have to learn each noun together with its article:

• de vergadering = the meeting

There is not always a simple rule that lets you predict de or het, so it is best to memorize the noun with the article.

In this sentence, werkplek means workspace, desk area, or workstation.

So mijn werkplek is my work area.

Depending on context, English workplace can mean the whole company or place of employment, but Dutch werkplek often feels more like the specific place where you work physically, such as your desk or station.

Yes, absolutely.

That version is also correct:

• Ik maak mijn werkplek schoon voordat de vergadering begint.

The meaning stays the same. The difference is mainly word order:

• Voordat de vergadering begint, maak ik mijn werkplek schoon.
  This emphasizes the time frame first.
• Ik maak mijn werkplek schoon voordat de vergadering begint.
  This starts with the action itself.

Both are natural Dutch.

Because the sentence starts with a subordinate clause:

• Voordat de vergadering begint,

Dutch normally places a comma between that opening clause and the main clause that follows:

• Voordat de vergadering begint, maak ik mijn werkplek schoon.

So the comma helps mark the boundary between the two parts of the sentence.