Efter et hurtigt brusebad bruger jeg tandtråd, før jeg går ud af badeværelset.

Because Danish main clauses normally follow the V2 rule: the finite verb comes in the second position.

In this sentence, Efter et hurtigt brusebad is placed first. That counts as the first element, so the verb bruger must come next:

Efter et hurtigt brusebad bruger jeg tandtråd

If the sentence started with the subject, then you would get:

Jeg bruger tandtråd efter et hurtigt brusebad

So the word order changes because the time phrase has been moved to the front.

Because før introduces a subordinate clause.

In Danish, subordinate clauses usually do not use the V2 pattern of main clauses. Instead, the subject normally comes before the verb:

før jeg går ud af badeværelset

So:

• main clause: bruger jeg
• subordinate clause: jeg går

That contrast is very typical in Danish.

Because brusebad is a neuter noun, so it takes the article et.

Also, when an adjective describes a neuter singular noun in the indefinite form, the adjective usually gets -t:

• et hurtigt brusebad
• et stort hus
• et koldt bad

If it were a common-gender noun, you would usually see en and the adjective without -t, for example:

• en hurtig morgen

So et hurtigt brusebad is just normal agreement.

Brusebad specifically means a shower.

It is more specific than bad, which can mean bath, wash, or bathing more generally depending on context.

So:

• et bad = a bath / a wash / bathing
• et brusebad = a shower

In this sentence, brusebad makes it completely clear that the person is taking a shower, not a bath.

Because tandtråd is being used in a general, uncountable way, like dental floss in English.

After a verb like bruge, Danish often uses the bare noun when talking about a substance, tool, or general activity:

• bruge tandtråd
• bruge sæbe
• bruge shampoo

So bruger jeg tandtråd means I use floss / I floss, not I use a floss.

Yes. It is a very natural way to express that idea in Danish.

Literally it means use dental floss, but in ordinary English that action is often just floss. Danish commonly keeps the noun:

bruge tandtråd

You may also hear other ways of expressing the idea, but bruge tandtråd is clear, normal, and common.

Ud af means out of.

So:

• gå = go / walk
• gå ud = go out
• gå ud af badeværelset = go out of the bathroom

This is a very natural Danish way to express leaving a room. English often uses leave the bathroom, but Danish frequently uses this kind of movement expression instead.

A more direct single-verb alternative would be forlade badeværelset, but that can sound a bit less everyday in this kind of context.

Because badeværelse is a neuter noun, and -et is the definite ending.

So:

• et badeværelse = a bathroom
• badeværelset = the bathroom

Danish usually puts definiteness on the end of the noun rather than using a separate word like English the.

Here it is the bathroom because it is a specific bathroom already understood from the situation.

Yes, in this sentence you usually can.

Both før and inden can mean before. So these are both natural:

• før jeg går ud af badeværelset
• inden jeg går ud af badeværelset

In many everyday contexts, the difference is very small. Some learners notice that inden can sometimes feel a bit more like before / by the time, but here either choice works well.

Because Danish comma usage allows some variation here.

Many writers would write the sentence without a comma:

Efter et hurtigt brusebad bruger jeg tandtråd før jeg går ud af badeværelset.

Others would include one:

Efter et hurtigt brusebad bruger jeg tandtråd, før jeg går ud af badeværelset.

So if you see both styles, that is normal. The version with the comma is very common in teaching materials because it makes the subordinate clause easier to see.

Yes.

For example, you could say:

Jeg bruger tandtråd efter et hurtigt brusebad, før jeg går ud af badeværelset.

That is grammatical too.

The version with Efter et hurtigt brusebad at the front sounds a bit more like the speaker is setting the scene or emphasizing the time sequence first. Danish allows this kind of flexibility, but the V2 rule still applies in the main clause.

Because efter and bagefter do different jobs.

Efter is a preposition, so it needs something after it:

• efter et hurtigt brusebad

Bagefter is an adverb, so it can stand more on its own:

• Jeg tager et hurtigt brusebad. Bagefter bruger jeg tandtråd.

So in this sentence, efter is the right choice because it introduces the noun phrase et hurtigt brusebad.