Learn German: Der Schauspieler ist immer müde, bevor das Stück anfängt. - The actor is always tired before the play begins.

The word bevor (before) is a subordinating conjunction. This means it introduces a dependent clause and kicks the conjugated verb to the very end of that section.

I learned that anfangen (to begin) is a separable verb. Why isn't it separated here?

You are right, anfangen normally separates in a main clause (like Das Stück fängt an). However, because bevor pushes the verb to the end of the sentence, the prefix (an-) and the main verb (fängt) are forced back together into one single word: anfängt.

Is the comma before bevor required?

Yes! In German, subordinate clauses (like the one starting with bevor) must be separated from the main clause by a comma. This is a strict rule, unlike in English where we usually don't use a comma before "before".

I thought das Stück meant "the piece". Why is it translated as "the play" here?

Das Stück literally translates to "the piece", but it is very commonly used as a short way to say das Theaterstück (the theatrical play). In the context of an actor (der Schauspieler), it is understood as "the play".