Learn Hardcore Dutch: De artiest wacht in de kleedkamer tot het optreden begint. - The artist waits in the dressing room until the performance begins.

The verb wachten is the infinitive (English: to wait). In the sentence you see wacht because it is the third-person singular present tense form, matching the subject de artiest (“the artist”). Dutch drops the -en ending in the present tense singular: ik wacht, jij wacht, hij/zij/het wacht.

Why is there no preposition op after wacht? I thought you always wait op something.

Dutch has two different constructions:

wachten op + noun means “to wait for something” (e.g. wachten op de bus).
wachten tot/totdat + clause means “to wait until something happens.”
Here you’re waiting until the performance begins, so you use wachten tot
- subordinate clause rather than wachten op.

Why is the preposition in used with de kleedkamer? Could I use op or naar instead?

in expresses being inside a place, and a dressing room is an enclosed space, so you say in de kleedkamer (“in the dressing room”).

op is used for surfaces or events (e.g. op het podium “on the stage”).
naar means “to” and would imply movement toward the dressing room: naar de kleedkamer gaan (“go to the dressing room”).

Why is kleedkamer written as one word, and what does it literally mean?

Dutch often forms compound nouns by combining words. kleedkamer merges kleed (“clothes”) + kamer (“room”), so it literally means “clothes room” and is used for “dressing room.”

Why does the verb begint appear at the end of tot het optreden begint?

In Dutch, subordinate clauses (introduced by conjunctions like tot or totdat) follow a verb-final word order. The conjugated verb moves to the very end of that clause: tot het optreden begint.

What’s the difference between tot and totdat? Can I use them interchangeably here?

tot is primarily a preposition (followed by a noun) but is often used colloquially as a conjunction before a clause.
totdat is the standard conjunction meaning “until” before a clause.
So you could also say totdat het optreden begint, which is more formal, but tot het optreden begint is very common in spoken and informal written Dutch.

Why do we say de artiest and de kleedkamer, but het optreden? How do I know when to use de vs het?

Dutch nouns belong to one of two grammatical genders:

Common gender (masculine/feminine) takes de (e.g. de artiest, de kleedkamer).
Neuter gender takes het (e.g. het optreden).
Unfortunately there’s no simple rule—you have to learn each noun’s gender. Dictionaries always list the article.

Why is it het optreden and not een optreden? When would you use een?

het is the definite article (“the”), used when speaking of a specific, known performance.
een is the indefinite article (“a”), which you would use if the performance were not yet identified or one of many, e.g. Een artiest wacht in de kleedkamer tot een optreden begint (a very general statement).

What’s the difference between voor, voordat, tot, and totdat for expressing time like “before” and “until”?

voor + noun means “before” in time: voor het optreden (“before the performance”).
voordat + clause means “before” with a verb clause: voordat het optreden begint.
tot + noun means “until” a moment: tot het optreden (“until the performance”).
totdat + clause means “until” with a verb clause: totdat het optreden begint.
In your sentence, you need “until the performance begins,” so you choose tot (or totdat) + subordinate clause.

Can I start the sentence with In de kleedkamer? If so, what changes in word order?

Yes. Dutch is a V2 (verb-second) language in main clauses, so if you bring In de kleedkamer to the front, you invert subject and verb: “In de kleedkamer wacht de artiest tot het optreden begint.”
Notice wacht stays second, then the subject de artiest follows.