Bevor Besuch kommt, fege ich den Flur und leere den Mülleimer aus.

Because bevor introduces a subordinate clause.

In German, subordinate clauses usually send the conjugated verb to the end:

• Bevor Besuch kommt
• weil ich keine Zeit habe
• wenn er nach Hause kommt

So kommt is at the end because Bevor Besuch kommt is not a main clause.

Because the sentence starts with the subordinate clause Bevor Besuch kommt. That whole clause takes up the first position in the sentence, so the conjugated verb of the main clause must come immediately after it.

German main clauses follow the verb-second rule:

• Ich fege den Flur.
• Bevor Besuch kommt, fege ich den Flur.

So the order becomes:

• first position: Bevor Besuch kommt
• second position: fege
• then: ich

This is a very common pattern in German.

Here, Besuch means something like visitors/company/guests coming over in a general sense. In this use, German often leaves out the article.

So:

• Bevor Besuch kommt = before company comes / before guests arrive

If you said der Besuch, it would sound more specific, like the visit or the guests already known from context.

Compare:

• Wir bekommen Besuch. = We’re having visitors.
• Der Besuch kommt um acht. = The visitors / the visit comes at eight.

Grammatically, Besuch is singular, which is why the verb is kommt, not kommen.

But semantically, it can refer to one or more visitors. It often works like a collective idea:

• Besuch kommt. = visitors are coming / company is coming

So even if several people are coming, German still commonly uses singular Besuch.

Both are direct objects, so they are in the accusative case.

The verbs are:

• den Flur fegen = to sweep the hallway
• den Mülleimer ausleeren = to empty the trash can

Both Flur and Mülleimer are masculine nouns:

• der Flur → accusative den Flur
• der Mülleimer → accusative den Mülleimer

So den here is the masculine accusative article.

Because the verb is ausleeren, which is a separable verb.

In a main clause, separable prefixes split off and go to the end:

• Ich leere den Mülleimer aus.

But in an infinitive or subordinate clause, the verb stays together:

• Ich will den Mülleimer ausleeren.
• ..., weil ich den Mülleimer ausleere.

So in your sentence, leere ... aus is exactly what we expect in a main clause.

Den Mülleimer ausleeren literally means to empty the trash can.

That is slightly different from English take out the trash, which often focuses on carrying the trash bag outside. German can express both ideas in different ways:

• den Mülleimer ausleeren = empty the trash can
• den Müll rausbringen = take the trash out
• den Mülleimer leeren = empty the trash can

So this sentence is specifically about emptying the bin, not necessarily about taking the garbage all the way outside.

Der Flur usually means hallway, corridor, or entry hall, depending on the building.

In a home, it often means the area near the entrance or the hall connecting rooms.

So:

• den Flur fegen = sweep the hallway / sweep the hall

The best English translation depends on the house or apartment layout.

Yes. In German, a subordinate clause is normally separated from the main clause by a comma.

So this is correct:

• Bevor Besuch kommt, fege ich den Flur und leere den Mülleimer aus.

That comma is required because Bevor Besuch kommt is a subordinate clause.

Yes, absolutely. That is also correct.

The difference is mostly in emphasis:

• Bevor Besuch kommt, fege ich den Flur ...
  This puts the time condition first: Before visitors come...
• Ich fege den Flur ..., bevor Besuch kommt.
  This starts with what you do, then adds before visitors come.

Both are natural German. The grammar changes slightly because the word order in the main clause stays normal when the main clause comes first:

• Ich fege ... not
• fege ich ...

Because both verbs share the same subject, ich.

So German does not need to repeat it:

• fege ich den Flur und leere den Mülleimer aus

This is the same idea as in English:

• I sweep the hallway and empty the trash can

You could repeat ich, but it would usually sound unnecessary here.